274 THE CEPHALOPODA. § 235. 



Spirula/'^ an analogous calcareous tube extends close upon the inner sur- 

 face of the shell from one septum to another. The animal, whose trunk 

 occupies only the first chamber, is loosely attached to it by the cartilaginous 

 border of its mantle. 



With Nautilus, this border has a lobe which extends along the back of 

 the animal, surrounding the spiral portion of the shell. <^^ With all the 

 Nautilina, there is another prolongation in the form of a membranous 

 tube, or Sipho, which arises from the posterior part of the body, — trav- 

 erses the orifices or calcareous tubes of the septa, and penetrates even into 

 the last chambers of the shell. These chambers are lined with a thin mem- 

 brane, and have no external communication except through the Siphon. 



2. With the Loligina, an internal shell lies free in the dorsal portion of 

 the mantle. In most genera, it is composed of a homogeneous, horny 

 substance, of a yellowish-brown color, and has a form like a feather 

 (Calamus), or the head of a lance. At one of its extremities is an attenu- 

 ated stem, and two delicate lateral winglets of variable length. *'> With 

 Sepia, this shell diifers very much from that of the other Loligina. Its 

 two surfaces are covered by very distinct calcareous layers, which have 

 erroneously given it the name of Os sepiae.^^^ As a whole, it is tongue- 

 shaped ; its two surfaces are convex and its borders are sharp. Behind, 

 the lateral borders become thinner and are slightly bent toward the ventral 

 surface ; and a short conical point projects from the middle of the pos- 

 terior border. The horny substance is reduced to a thin sheet, situated 

 between the calcareous layers, but its borders usually extend out beyond 

 those of these last. The calcareous layer of the dorsal surface is very 

 thin, but quite solid, and its surface in front, is granulated and striated; 

 that of the ventral surface, on the other hand, is very thick, especially 

 in the middle, and its very loose tissue contains numerous quite thin, 

 porous lamellae, which, superposed almost horizontally, alternate regularly 

 with layers of small, transversely-striated, dichotomous, vertical prisms."'^ 

 This ventral layer is truncated obliquely from its middle backwards, and 

 the horizontal layers may easily be counted upon its truncated surface. '**> 



3 De Blainvitle, Ibid. p. 18, PI. I. fig. 6, A-P. might well have been the male of certain Ammo 



* Owen, and Valenciennes, loc. cit. nites." If the relations of the Ilectocotyli to cer- 



5 See Wagner, Icon. zoot. Tab. XXIX. fig. 32 tain Octopoda are borne in mind, the idea of 



{Loligo), and Ferussac, loc. cit. {LoHgo, Loli- Braun, that there have existed Ammonites, the 



gopsis, Onychoteuthis, Sepiola, and Sepioteu- males of which are quite different in form from the 



this). females, certainly merits much consideration. For 



I cannot here omit speaking of the remains of an the males of these animals were, perliaps, abortive 



antediluvian animal, which, under the name of like those of Argonauta and Tremoctopus, and 



Aptyc/ius, has much engaged the attention of pa- obliged, therefore, to shelter themselves in the man- 



laeontologists, and, up to the present time, been the tie of their females, and this would explain why it is 



object of discussion. that the specimens of Aptychus are so often found 



Some have regarded it as the operculum of an at the base of the first chamber of Ammonites. 



Ammonite or of another MoUusk {Ruppe/l, Abbild. Judging from the form of the shell, the bodies of 



und Beschreib. einig. Versteiner. von Solenhofen, these animals must have been very large. There 



1829, and Voltz, in the Neuen Jahrbuch fiir Slin- will be an additional analogy in favor of this view, 



eralogie, &c., 1837, p. 304, 432) ; others as a shell if it is proved that the large and flattened animal 



of a bivalve {H. von Meyer, in the Nov. Act. found by Qmoj/ and Gaimard is really the male of 



Acad. Nat. Cur. XV. pt. II. p. 125 and in the a Nautilus (§. 233, note 3). 



Jahrbuch f. Mineral. &c. 1831, p. 391) ; and oth- G The error of Spix (Cephalogenesis, loc. cit. p. 



ers, finally, as an internal shell of one of the Oeph- 33) in comjiaring it to a rudimentary vertebral 



alopoda {Coquand, in the Bull, de laSoc. Geol. de column, is still wider. 



France, XII. 1840-41, p. 376). 'i According to Kolliker (Entwickel. loc. cit. p. 

 This last opinion is undoubtedly the correct one. 72, Taf. V. fig. 45, 46) these calcareous prisms be- 

 As for myself, I am able to perceive in the different gin to be formed in the embryo. 

 Bpecies of Aptychus only shells whose shaft isabor- 8 A vei'y detailed description of this Os sepiae 

 live, and the wings excessively develi)j>ed. 1 was has been given by Cuvier (Mem. loo. cit. p. 46), 

 therefore quite surprised to hear my colleague, Al- Brandt (.Mediz. Zool. II. p. 301, Taf. XXXI. fig. 3, 

 r.vander Braun, express hhnsM in a conversation, (i), Wagner (Icnn. zoot. Tab. X.X^IX. fig. 34), and 

 Uiat, "after all, the animal called Aptychus Ferussac (loc. cit.). 



