Lamarck constitutes many genera of the shells included in the Ostrea genus of Linnæus. His Malléacées comprehend five genera, Crenatula, Perna, Malleus, Avicula, and Meleagrina, all which are allied more or less remotely to the shell before us. To that particular family which is known among collectors by the designation of Hammer Oysters, he gives the name of Malleus, in the French Marteau, both alike implying the hammer like form of the species Malleus, which Lamarck assumes as the type of this genus. But even there after all the renovation that has been attempted, the result is not satisfactory, because this figure is by no means constant, even in the few species included by its author in that genus; it contains but six species, and these are entirely at variance with each other. Thus for example, in Malleus Vulgaris, the common Hammer Shell, we have a species with three lobes, a lateral one of considerable size being advanced on each side the beaks: and another shell of the same species with only short lateral lobes instead of large ones. Admitting the hammer form to be still preserved in these, in the next species, Malleus Normalis, instead of two lobes, the hammer head, if it may be so expressed, has but a single lobe: in Malleus Anatinus there is only one lobe, and that very small; and in Malleus Vulsellatus, although characterised as “lobo oblique porrecto,” the appearance of the shell implies rather the total absence of any lobe, for the lobe, if so it may be termed, is so indefinite, that it cannot be referred without violence to the genus Marteau, while we consider its hammer like form as a leading character of the genus. With exception to this inconstant character which may be qualified with the expression “deformed and generally hammer shaped,” we have no objection to the Malleus genus, because the byssus of the animal by means of which it can affix itself to other bodies, and the peculiar sinus or sulcation of the hinge through which the byssus passes from the animal to those extraneous bodies, are sufficient to remove it from the Ostrea genus, in which case if we still adhere to the Linnæan method we can place it only among his Mytili or Pinnæ, and it has certainly less affinity with either of those than with Ostrea. Perhaps the name of Perna under which this shell has been mentioned a few years ago might have been as well preserved, but that name Lamarck assigns to an extensive genus of which Ostrea Isognomum is the type, and it is therefore better to retain the name Malleus than to alter it to another which could not fail at this time to create confusion. The same consequence would as unquestionably result were we to sub-divide the Malléacées into different genera according to the configuration of the shell or number of its lateral lobes.
The definition of Malleus in the Règne Animal of Cuvier appears to intimate the same objection; it does not consider the hammer like form of the shell as any criterion, it is only stated that the Marteaux are inequivalve and irregular, that they have a simple hollow for the ligament as in the oysters, but that they are distinguished by a slope at the side of the ligament for the passage of the byssus.
It is assuredly true that the presence of a byssus in this tribe of shells displaces them from any immediate analogy with the Ostrea, where as Cuvier remarks “Linnæus left them.” But, if however, we attentively examine the hinge of the common oyster, the two valves, and the oyster as it lies within the valves, we shall perceive with this exception a pretty near approximation. The great objection is, that the animal of the tribe of shells now before us protrudes a byssus from its body through a lateral opening on one side or slope of the ligament of the hinge; if we closely inspect the valves of the oyster, we also find a slight depression or hollow upon each side of the cartilage of the hinge; these are small, and usually somewhat lamellar. The oyster, moreover, as it lies in the shell, seems capable of expanding or spreading that part of the body which lies under the hinge laterally upon and into these depressions, a circumstance very easily observed in the half famished oyster, because these lateral expansions of the animal are then more visibly elongated along the passage of these lateral grooves of the hinge, and give the pointed end of the animal a somewhat cornuted appearance. Under the same circumstance these processes adhere as they lie in the hollow of these grooves, and thus suggests the idea of the animal having exerted itself by such extension to obtain refreshment through these lateral hollows. Those hollows are also so far pervious as to admit the ingress of moisture while the shells are closed, in the same manner as it is possible the Malleus genus may receive moisture under the same circumstance through the sinus, whence the byssus is protruded. These peculiarities considered, may perhaps afford some further justification of Linnæus in placing the hammer shells with the Ostreæ. It has been indeed advanced that Linnæus was not aware of these hammer shells being furnished with a byssus, or that he would have referred them to the Mytili, but this observation cannot be correct, because in the figure given of these shells by Seba, to which Linnæus refers, the byssus, which is very conspicuous, is represented pendent or hanging to a considerable length out of the shell.
From an attentive examination of the different Conchological authors, it does not appear to us that the shell before us has hitherto been figured, and we have reason also to believe that it has never been described. These circumstances are the more probable since, as we have before observed, the shell is at this time very little known among the Continental Cabinets. The nearest approach, so far as we can judge from the description, unassisted by any figure, is the Marteau Normal (Malleus Normalis) of Lamarck, a species defined by him as testa biloba; lobo basis unico anticali ad normam, our shell is certainly bilobate, for it has only one lateral lobe at the beak, and that moreover advances from the beak, pretty nearly, though not exactly, in a right line; but its general description does not sufficiently accord with our shell to authorise as a conclusion that they are the same. Lamarck informs us that there are two varieties of his Malleus Normalis, one of which is a native of the ocean of the Great Indies, the other of the seas of New Holland. The first, or Indian kind, he describes as being on the inside as well as outside of a black colour, with a longish lobe at the base of the shell.[[22]] The New Holland kind is described of a whitish colour, with the lobe at the base abbreviated.[[23]]
The two last-mentioned shells which Lamarck concludes to be varieties of the same species, may perhaps prove hereafter to be species distinct from each other, as Lamarck has himself shewn to be the case with respect to the common black and the white hammer shells. The black supposed variety of Malleus Normalis we apprehend to be distinct from the shell before us, but it is possible that the New Holland shell which he describes as being whitish, with the lobe at the base abbreviated, may be a worn or much depauperated specimen of our present shell; it certainly does not accord with our shell in any tolerable state of preservation.
Lamarck says nothing of any ruddiness or testaceous hues in his New Holland variety of Normalis, and admitting these colours to indicate that the shell had been found with its animal in a living state, we can scarcely conceive the dark fuscous spotting which is so conspicuous in the species could by any ordinary accident be so entirely obliterated as appears to be the case in Lamarck’s specimen, if his New Holland variety of Malleus Normalis be really of this species; and it may be further added that if our present shell was actually intended by his Malleus Normalis, the defects of his shell has necessarily influenced his specific character and rendered it imperfect.
We have not adverted to Malleus Anatinus of Chemnitz, because the figure of that shell is ambiguous. There is a remote resemblance in the lateral appendages of the beaks, but in other particulars the resemblance is less obvious, the body is sometimes curved as in the shell before us and sometimes straight, but the edges of the valves are parallel, and the shell itself pellucid: the figure in Chemnitz is less than half the size of our shell. This inhabits the seas of Timor and the Nicobar Islands.
It should be observed in conclusion that there is a specimen of our species among the Hammer Shells in the British Museum, the habitat of which is indicated by the word “Amboina:” it is much smaller than our shell. Besides this we have lately seen another example from New Holland, of a growth still larger than the shell we have delineated.
We have entered thus minutely into the analogies of this shell from an apprehension we might otherwise in this instance submit as a new species an object that had been previously described. The result of our enquiry will tend to shew that if the species has not remained entirely unnoticed, it has never been described with much precision.