314 



CEPllALOrODA.- 



-MOLLUSCA.- 



-Decapoda. 



careous. Tlie head is smaller than the body, and the 

 eyes are free in the orbit, turning in every direction in 

 the very large orbital cavity. The arms are usually 

 said to be ten in number — hence their name of Deca- 

 pods. Two of these, however, ditl'er considerably in 

 their form from the others, and by many conchologists 

 are termed tentacles. The real arras are eight in 

 number, as in the Ootopods, but are always shorter; 

 they are fleshy, sessile, and often edged witli mem- 

 branes. The two tentacular arms are long, cylindrical 

 and are expanded at the ends. The cups or suckers 

 are oblique, pedunoled, and armed with a homj' ring. 

 The siphunele is almost always provided with an 

 internal valve. The animals belonging to this sub- 

 order are cliietly found in the open sea, but, it is said, 

 make their appearance periodically in large slioals, like 

 certain fishes, on the coasts and banks. The structure 

 of tlie internal shell is well adapted for dividing the 

 species of Decapods into three distinct groups or sec- 

 tions — those which have a solid horny shell, like a 

 pen {(jladius), CnoNDitoPHORA ; those which have a 

 cellular calcareous shell {sepion}, Sefiopiioua ; and 

 Jnstly, those which have a chambered, siphoned shell, 

 (in recent species) calcareous or shelly, Belemno- 



I'lIORA. 



Section I.— CHONDROPHORA. 



This section contains five families, but we have 

 only space to mention two : — i 



Family I.— CHIU0TEUTHID-3E. 



The animals of this family are semipellucid, and 

 have an elongate body, and the fins are placed on tlie 

 hinder part of the back. The ventral arms are long, 

 and the tentacular arms are external to the web, very 

 long and slender, and not retractile into the cavities 

 under the orbits. On the peduncular portion they 

 have distant sessile cups, but on their expanded ends 

 they possess four rows of cups placed on long cylin- 

 drical peduncles. The siphuncle has no valve. Tlie 

 shell is elongated and slender. 



Genus Chiroteutiiis. — The genus Chiroteutkis 

 will represent the family. It has the arms free ,; the 

 rings of the cups are contracted in the middle. The 

 tentacular arms are extremely elongated, and the cups 

 on their expanded ends are placed on long cylindrical 

 peduncles swollen at the end, and bear a second pedicle 

 which carries a hood-like horny ring, edged at the 

 base, with a lateral aperture armed with teeth. The 

 shell is very slender, and slightly dilated into a narrow 

 lanceolate expansion at each end. 



CHIROTEUTHIS VERAlfyi, one of the species, is a 

 native of the Mediterranean. The body is scarcely 

 four inches in length, while the tentacular arms are two 

 feet and a half, and as slender as a thread. The habits 

 of this animal appear in a great measure unknown ; but, 

 as has been well observed, a similar disproportion of 

 parts is not to be found exampled among organized 

 creatures. " How these slender organs are moved," 

 says Dr. Johnston — "how their motions are propagated 

 along the lengthened line — how the club at the end of 



such a flexible hne is supported — and how the organs 

 are preserved from amputation or injury — are all 

 questions which start upon us as we contemplate the 

 creature, and to which it is not easy to give a satis- 

 ftictory answer." They are no doubt intended, and 

 certainly appear admirably adapted for securing their 

 prey, especially such as may be floating careless at a 

 distance, and unconscious of danger from such a foe. 



Family II.— ONYCHOTEUTHID^ {Uncinated 

 Calamaries) . 



This family consists of animals with an elongate fleshy 

 body, furnished with fins on the hinder part of the back. 

 The head is cylindrical in shape, and the eyes are naked, 

 with a deep lachrymal sinus at the upper edge. The 

 siphuncle has a distinct internal valve, and the ten- 

 tacular arms have a rounded group of small sessile cups 

 at their dilated extremities. The shell is lanceolate. 

 One of the most striking characters of this family is the 

 structure of the long tentacular arms and their suckers. 

 These organs are provided with a double series of 

 hooka ; but besides these uncinated cups there is, 

 as mentioned above, at the base of their expanded 

 extremities a cluster of small, simple, unarmed cups. 

 These they are supposed to unite, so that the tentacles 

 are used in conjunction. " When these suckers are 

 applied to one another," says Professor Owen, "the 

 tentacles are firmly locked together at that part, and 

 the united strength of both the elongated peduncles can 

 be applied to drag towards the mouth any resisting 

 object wdiich has been grappled by the terminal hooks. 

 There is no mechanical contrivance which surpasses 

 this structure : art has remotely imitated it in the 

 fabrication of the obstetrical forceps, in which either 

 blade can be used separately, or by the interlocking 

 of a temporary joint be made to act in combination." 

 This family contains several genera, but we have only 

 space to mention two :— 



Genus Enoploteuthis. — This genus has both the 

 sessile and tentacular cups armed with claw-like hooks. 

 It contains several species with an elongate body fur- 

 nished with fins on the hinder part of the back; sessile 

 arms with a series of closed, horny, claw-like hooks, 

 enlarged at their base and covered with a closely-fitting 

 retractile membrane ; tentacular arms slender, feeble, 

 scarcely dilated at the ends, and armed with hooks only. 

 Some of the species attain a large size, and the natives 

 of the Polynesian islands, who dive for shell-fish, are 

 said to have a well-founded dread and abhorrence of 

 tnese formidable creatures. A specimen of E. ungui- 

 culata was observed by Banks and Solander, in Captain 

 Cook's first voyage, floating on the surface in the Pacific 

 Ocean, a single arm of which is preserved in the collec- 

 tion of the Museum of the College of Surgeons, from 

 which it is evident that the animal must have been at 

 least six feet long. 



Genus Ommastrephes. — This genus is character- 

 ized by having the body very long, acuminated behind, 

 truncated and square in front, with very broad terminal 

 fins; sessUe armSjWith two rows of suckers having obli(]ue, 

 toothed rings ; tentacular arms short, thick, and strong, 

 not retractile, webbed at the slightly enlarged extremity, 



