114 



MOLLUSCA. 



hare a picture of the Star-fish. Professor Owen has observed, 

 moreover, that the tentacles of the Pearly Nautilus lead to the antennae 

 of Articulates. On account of these peculiarities, Vogt separates the 

 the Cephalopods into a distinct primary division of the Animal King- 

 dom. Agassiz says it is easy to homologize all the systems of the organs 

 with those of other Molluscs : the differences constitute only class char- 

 ters and exhibit in no way a different phase. 



Cephalodods are marine and carnivorous ; nocturnal and social ; 

 oviparous and bisexual — the females being larger and more numerous 

 than the males. The locomotive organs are attached to the head. Unlike 

 most other Molluscs, they are symmetrical ; and the shell is usually 

 straight or coiled in a vertical plane, instead of being spiral as in the 

 unsymmetrical Gastropods. The Nautilus and Argonaut alone of living 

 tribes have external shells ; the rest are naked. 



Order I. — Dibranchiata. 



The members of this Order, with the single exception of the Argonaut, 

 have an internal shell which is sometimes called the skeleton, but has 

 nothing to do with protecting the nervous centres. In lieu of an exter- 

 nal covering, they have eight or ten powerful arms furnished with suck- 

 ers, more perfect organs of vision, more vigorous circulation, and the 

 power to secrete an inky fluid with which to cover their retreat. The 

 Cuttle-fish is the largest of all animals not supported by a jointed skele- 

 ton. The Order first appeared in the Lias. 



No. 456. Belemnites Owenii, Pratt. 



Gttahd. The Belemnite is the most complicated of Cepha- 

 lopod shells. The chambered part or phraymocone (represented 

 by the terminal appendix of the Squid), is a straight attenuated 

 cone 'with numerous septa, resembling a pile of watch-glasses, 

 concave towards the base. The whole is enveloped in a sheath ; 

 and the two together are lodged in a conical cavity or alveolus 

 excavated in the base of a long spathose body (corresponding to 

 the mucro of the cuttle-bone), resembling the head of ajavelin, 

 whence the generic name. The exterior of this " guard," as it 

 is called, has usually a longitudinal groove ; and the septa of the 

 phragmocone are perforated by a marginal siphuncle generally 

 situated on the side nearest the groove ; but in certain species, 

 characterized by a flattened guard, the siphuncle is on the oppo 

 site side. Besides these fossil parts, there have been found 

 remains of the ink-bag, pen, mantle, fins, mandibles, arms and 

 hooks. This specimen, now in the Ward Museum of the Uni 

 versity of Rochester, is from the Oxford Clay (Upper Oolite). 

 Christian Malford, England. The fractured upper portion shows the alveolar 

 cavity with the phragmocone in place. Size, 6x3. Price, $0.60. 



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