MOLLUSCA 



133 



Section b. Dccapoda Owitdrophora. 

 Character. Internal shell horny. 



Sub-section o. Myopsidx (d'Orb.). 



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

 touch the lens ; mostly frequenters of the coast. 

 Family 1. Loligidse. 



Genera : Loligo, Schneid. (figs. 99, &c. ) ; Loliolus, Steenstrup ; 

 Sqnoteuthis, Blv. ; [Teuthopsis], Desl. ; [Leptoteuthis], Meyer; 

 [Selemnosepia], Ag. ; [Eelotevthis], Munst. 

 Family 2. Sepiolidx. 

 Genera : Sepiola, Schneid. ; Bossia, Owen. 



Sub-section fi.Oigopsida (d'Orb.). 



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

 anterior surface of the lens ; mostly pelagic animals. 

 Family 3. Crandiiadas. 



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

 Family 4. Loligopsidse. 



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

 Family 5. Cheiroteuthidee. 



Genera : Cheiroteuthis, d'Orb. (fig. 93. A) ; Histioleuthis, d'Orb. 

 Family 6. Thysanoteutiiidse. 



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

 Family 7. Onydwteuthidss. 



Genera : Gonatus, Gray ; OnychoteuUiis, Lichtenst (fig. 97) ; Ony- 

 cJiia, Lesneur ; EnaplotevOiis, d'Orb. , Veranya, Krohn ; [Plesio- 

 teuthis], A. Wag. ; [Cel&ito], Miinst. ; Dosidicus, Steenstrnp ; 

 Ommastrephes, d'Orb. 



Sub-order 2. Octopoda. 



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

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



D 



FIG. 94. Octopodous Siphonopods ; one-fourth the natural size linear. A. 

 Pinruxioput cordiformis, Qaoy and Gain (from New Zealand). B. Tremac- 

 topus tialaixas, Ver. (from the Mediterranean). C. Cranchia soabra, Owen 

 (from the Atlantic Ocean ; one of the Decapoda). D. Cirrhoteuthis iKUtri, 

 Esch. (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. Ko buccal membrane surrounds the mouth. 

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

 no nidamental glands. The viscero-perieardial 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. 

 Family 1. CirrJiokv.(hid&. 



Genus : CirrhoteutJiis, Esch. (Sciadtphorus, Reinh.) (fig. 94, D). 

 Family 2. Octopodidas. 



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

 Soeurgitf, Trosch. ; Eltdone, Leach ; Bolitxna, Steenstrup. 



Family 3. Pkilonexidas. 



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

 B) ; Parasira, Steenstrup (Octopus catenulatus, Fer., is the 

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

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



B 



FIG. 95. A. Male specimen of Octopta yranlandieut, with the third arm of the 

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

 Sepia. 



Further Remarks 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 for 

 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 Nautilus pompUius, 

 lately purchased for the Museum 

 of University College, London. 



Visceral Hump and ShtU. 

 The visceral hump of Nautilus 

 (if we exclude from considera- 

 tion the fine siphuncular pedicle FIG %. Male of Parasim mttnu- 

 Which it trails, as it were, behind **- Steenstrup, (Orfp arena, 



it) is very little, if at all, affected 

 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 



Ver.), showing the hectocotylized 

 arm. ft, (2, f>, t*, the first, second, 

 third, and fourth arms or pro- 

 cesses of the fore-foot; A, the 

 third arm of the right side hecto- 

 cotylized; i, the apical sac of the 

 hectocotylized arm; y, the fila- 

 ment which issues from the sac 

 when development is complete ; 

 f, the siphon. (From Gegenbaur.) 



