[CHAPTER XII.]
FOSSIL CEPHALOPODA; COMPRISING THE BELEMNITIDÆ, NAUTILIDÆ, AND AMMONITIDÆ.
Lign. 140. Fossil Sepia or Cuttle-Fish: 1/3 nat. (M. D’Orbigny.)
Solenhofen.
(Kelæno[398] speciosa. Count Münster.)
The impression of the body, head, and arms, with their clasps.
[398] Kelæno (one of the Furies) = Acanthoteuthis (Wagner); probably identical with Belemnoteuthis, which also has ten sub-equal arms.—Mr. Woodward.
FOSSIL CEPHALOPODA
The molluscous animals named Cephalopoda (from their organs of prehension being arranged around the upper part of the body) are the most ancient, numerous, and interesting of this division of animated nature; and their fossil remains comprehend the most varied and striking forms of extinct beings that occur in the sedimentary strata, from the earliest Secondary to the latest Tertiary formations. The living species are but a feeble representation of the countless myriads which swarmed in the ancient seas; yet they afford important assistance in developing the characters of the numerous extinct genera, whose relics abound in the strata, and will continually be presented to the observation of the collector. It is therefore necessary to enter somewhat in detail on the structure of these beings, that the student may obtain a correct idea of the nature of the curious fossils to which the mineralized remains of the durable parts of these animals have given rise, and whose origin has but lately been correctly ascertained. The body of these mollusca is either enclosed in a shell, as in the Nautilus, or contains a calcareous or cartilaginous part, as in the Sepia, or cuttle-fish; they have a distinct head, and eyes as perfect as in the vertebrate animals; complicated organs of hearing; and a powerful manducatory apparatus, surrounded by arms serving for prehension. They have below the head a tube which acts as a locomotive instrument to propel the animal backwards, by the forcible ejection of the water that has served the purposes of respiration, and which can be thrown out with considerable force by the contraction of the body. The figures 1 and 6, [Lign. 142], are views of a naked (that is, shell-less) cephalopod, showing the arms, eyes, and a pair of fins, for swimming. The Cephalopoda, thus endowed with powerful organs of locomotion, traverse the seas unrestricted, and are seen in groups of myriads in the midst of the ocean, and only appear periodically near the shores. Their fossil remains consist of—
1st. The external shells; which are generally symmetrical, and either straight (as in Orthoceras, [Lign. 155]); arched or bent (as in Crioceras, [Lign. 160]); spiral (as in Turrilites, [Lign. 163]); or involute,[399] and simple (as in the Argonaut), or divided, by smooth or foliaceous partitions, into chambers or air-cells, connected by a hydraulic tube or siphuncle (as in Nautilus, Lign. [149] and [150], and Ammonites, [Lign. 156 and 157]).
[399] Involute, as applied to the shells of Cephalopoda, implies that the inner whorls are embraced by the outer turn or whorl; convolute, the inner turns apparent, or exposed; evolute, the whorls coiled in one plane, but not touching each other; revolute, the extremities bent inwards.