MOLLUSCA 



133 



Section h. — Decapoda Chond/rophora. 

 Character. — Internal shell horny. 



Sub-section a. — Myopsidm (d'Orb.). 

 Eye with closed cornea, so that the surrounding water does not 

 touch the lens ; mostly freijuenters of the coast. 

 Family 1. — Loligidm. 



Genera: Loligo, Sohneid. (figs. 99, &c.); LoUolus, Steenstrup ; 

 Blv. ; l^Teuthopsis], Desl. ; [Leptoteufhisl, Meyer ; 

 ^g- ) [Beloteutfds\, Miinst. 

 Family 2. — Sepiolidai. 

 Genera : Sepiola, Schneid. ; Rossia, Owen. ^ 



Sub-section (9. — Oigopsidss (d'Orb.). 

 Eye with open cornea, so that the surrounding water bathes the 

 anterior surface of the lens ; mostly pelagic animals. 

 Family 3. — Oranchiadse. 



Genus : Cranchia, Leach (fig. 94, C). 

 Family 4. — Loligopsidse. 



Genus : LoUgopsis, Lam. (fig. 93, C). 

 Family 5. — Cheiroteuthidss. 



Genera : Oheiroteuthis, d'Orb. (fig. 93, A) ; Sisiioteuthis, d'Orb. 

 Family 6. — Thysa/noteuthidas. 



Genus : Thysanoteuthis, Troschel (fig. 93, B). 

 Family 7. — Omyehoteuthidas. 



Genera : Gonatus, Gray ; OnychoUuthis, Liohtenst. (fig. 97) ; Ony- 

 chia, Lesueur ; Enoploteuthis, d'Orb. , Veranya, Erohn ; [Plesio- 

 teuthis], A. Wag. ; [Celssno], Miinst. ; Dosidicus, Steenstrup ; 

 " d'Orb. 



Sub-order 2. — Octopoda. 

 Characters. — Dibranchiata with the fore-foot drawn out into eight 

 arms only; suckers sessile, devoid of homy ring ; eyes small, the 



Fig. 94. — Octopodous Siphonopods ; one-fourth the natural size linear, A. 

 Firmoctopus corMformis, Quoy and Gain (from New Zealand). B. Tremoc- 

 topm violmxus, Ver. (from the Mediterranean). C. Cranckia scdbra, Owen 

 (from the Atlantto Ocean ; one of the Decapoda). D. CirrhoteutMs MiiUeri, 

 Esoh. (from the Greenland coast). 



outer skin can be closed over them by a sphincter-like movement. 

 The body is short and rounded ; the mantle has no cartilaginous 

 locking apparatus, and is always fused to the head dorsally by a 

 broad nuchal band. No buccal membrane surrounds the mouth. 

 The siphon is devoid of valves. The oviducts are paired ; there are 

 no nidamental glands. The viscero-pericardial space is reduced to 

 two narrow canals, passing from the nephridia to the capsule of the 

 genital gland. There is no shell on or in the visceral hump. 

 FamUy 1. — Oirrhoteuthidm. 



Genus: Cirrhoteuthis, Esch. [Sdadephorus, Ueaih.) (fig. 94, D). 

 Family 2. — Octopodidse. 



Genera : Pinnoctopus, d'Orb. (fig. 94, A) ; Octopus, Lam. (fig. 95) ; 

 Scaurgws, Trosoh. ; Eledone, Leach ; Bolitsena, Steenstrup. 



Family 3. — Philonexids. 

 Genera: Tremoctopus, Delle Chiaje {Philonexis, d'Orb.) (fig. 94, 

 B) ; Parasira, Steenstrup {Octopiis catenulatus, Fer., is the 

 female, and Octopus carena, Ver., is the male of the one species 

 of this genus according to Steenstrup (fig. 96)) ; Argonavia, L. 

 (the shell of this genus is formed only in the female by the 

 expanded ends of the two large " arms " of the fore-foot). 



Fig. 95. — A. Male specimen of Octopus grtxrdandicus, with the third arm of the 

 right side hectocotyUzed. B. Enlarged view of the hectocotylized arm of 



Further Remarhs on the Cephalopoda. — In order to give 

 a more precise conception of the organization of the Cephalo- 

 poda in a concrete form we select the Pearly Nautilus fov 

 further description, and in pass- 

 ing its structure in review we 

 shall take the opportunity of 

 comparing here and there the 

 peculiarities presented by that 

 animal with those obtaining in 

 allied forms. In the last edition 

 of this work the Pearly Nautilus 

 was made the subject of a de- 

 tailed exposition by Professor 

 Owen, and it has seemed accord- 

 ingly appropriate that it should 

 be somewhat fully treated on 

 the present occasion also. The 

 figures which illustrate the pre- 

 sent description are (excepting 

 fig. 89) original, and prepared 

 from dissections (made under the 

 direction of the writer) of a male 

 and female Jfautilus pompilius, 

 lately purchased for the Museum 

 of University College, London. 



Visceral Hump and Shell. — 

 The visceral hump of Nautilus 

 (if we exclude from considera- 

 tion the fine siphuncular pedicle Fio. 96.— Male of Parasira catenu- 



which it trails, as it were, behind ^^l^^^l^fSS.^^ 

 it) is very little, if at all, affected aim. (i, if, «3 «<, the first, second, 

 by the coiled form of the shell 

 which it carries, since the animal 

 always slips forward in the shell 

 as it grows, and inhabits a cham- 

 ber which is practically cylindri- 

 cal(fig. 89). Were the deserted chambers thrown off instead 

 of being accumulated behind the inhabited chamber as a 

 coiled series of air-chambers, we should have a more correct 

 indication in the shell of the extent and form of the animal's 



third, and fourth arms or pro- 

 cesses of the fore-foot; h, the 

 third arm of the right side hecto- 

 cotylized ; X, iihe apical sac of the 

 hectocotylized arm; y, the fila- 

 ment which issues from the sac 

 when development is complete ; 

 i, the siphon. (From Gegenbaur.) 



