Organs of hearing have been clearly ascertained to exist, mot only in fishes[3851], but in mollusca. In the oyster the presence of an acoustic apparatus of the simplest possible construction has been established by the discoveries of Siebold[3852], and from our knowledge of the reciprocal relations existing between the faculties of hearing and of producing sounds, the ascertained existence of the one affords legitimate grounds for inferring the coexistence of the other in animals of the same class.[3853]
Besides, it has been clearly established, that one at least of the gasteropoda is furnished with the power of producing sounds. Dr. Grant, in 1826, communicated to the Edinburgh Philosophical Society the fact, that on placing some specimens of the Tritonia arborescens in a glass vessel filled with sea water, his attention was attracted by a noise which he ascertained to proceed from these mollusca. It resembled the "clink" of a steel wire on the side of the jar, one stroke only being given at a time, and repeated at short intervals.[3854]
The affinity of structure between the Tritonia and the mollusca inhabiting the shells brought to me at Batticaloa, might justify the belief of the natives of Ceylon, that the latter are the authors of the sounds I heard; and the description of those emitted by the former as given by Dr. Grant, so nearly resemble them, that I have always regretted my inability, on the occasion of my visits to Batticaloa, to investigate the subject more narrowly. At subsequent periods I have since renewed my efforts, but without success, to obtain specimens or observations of the habits of the living mollusca.
The only species afterwards sent to me were Cerithia; but no vigilance sufficed to catch the desired sounds, and I still hesitate to accept the dictum of the fishermen, as the same mollusc abounds in all the other brackish estuaries on the coast; and it would be singular, if true, that the phenomenon of its uttering a musical note should be confined to a single spot in the lagoon of Batticaloa.[3861]
Although naturalists have long been familiar with the marine testacea of Ceylon, no successful attempt has yet been made to form a classified catalogue of the species; and I am indebted to the eminent conchologist, Mr. Sylvanus Hanley, for the list which accompanies this notice.
In drawing it up, Mr. Hanley observes that he found it a task of more difficulty than would at first be surmised, owing to the almost total absence of reliable data from which to construct it. Three sources were available: collections formed by resident naturalists, the contents of the well-known satin-wood boxes prepared at Trincomalie, and the laborious elimination of locality from the habitats ascribed to all the known species in the multitude of works on conchology in general.
But, unfortunately, the first resource proved fallacious. There is no large collection in this country composed exclusively of Ceylon shells;—and as the very few cabinets rich in the marine treasures of the island have been filled as much by purchase as by personal exertion, there is an absence of the requisite confidence that all professing to be Singhalese have been actually captured in the island and its waters.
The cabinets arranged by the native dealers, though professing to contain the productions of Ceylon, include shells which have been obtained from other islands in the Indian seas; and the information contained in books, probably from these very circumstances, is either obscure or deceptive. The old writers content themselves with assigning to any particular shell the too-comprehensive habitat of "the Indian Ocean," and seldom discriminate between a specimen from Ceylon and one from the Eastern Archipelago or Hindustan. In a very few instances, Ceylon has been indicated with precision as the habitat of particular shells, but even here the views of specific essentials adopted by modern conchologists, and the subdivisions established in consequence, leave us in doubt for which of the described forms the collective locality should be retained.
Valuable notices of Ceylon shells are to be found in detached papers, in periodicals, and in the scientific surveys of exploring voyages. The authentic facts embodied in the monographs of REEVE, KUSTER, SOWERBY, and KIENER, have greatly enlarged our knowledge of the marine testacea; and the land and fresh-water mollusca have been similarly illustrated by the contributions of BENSON and LAYARD to the Annals of Natural History.
The dredge has been used, but only in a few insulated spots along the coasts of Ceylon; European explorers have been rare; and the natives, anxious only to secure the showy and saleable shells of the sea, have neglected the less attractive ones of the land and the lakes. Hence Mr. Hanley finds it necessary to premise that the list appended, although the result of infinite labour and research, is less satisfactory than could have been wished. "It is offered," he says, "with diffidence, not pretending to the merit of completeness as a shell-fauna of the island, but rather as a form, which the zeal of other collectors may hereafter elaborate and fill up."