114 Prof. E. J. Chapman on the Occurrence of 



and which, by being rolled up against the side of the arm, forms 

 a furrow or canal; c, the commencement of this furrow ; d, an 

 angular fold of skin, which separates the acetabuliferous portion 

 from the apical plate. 



Fig. 3. Octopus, sp. indeterm. S . Third right arm, with a portion of the 

 fourth right arm. Half the natural size. 



Fig. 4. Octopus, sp. nov. S • The apex of the third right arm. Natural size. 



Fig. 5. Eledone moschata, Leach. ^ . Third right arm, half the natural size. 



Fig. b'. Its apex, somewhat enlarged. 



Fig. 5". The apex of one of the seven other arms of the male, slightly 

 enlarged. 



Fig. 6. Eledone cirrosa, Lamk. <? . A piece of the apex of an arm of the 

 male. 



Fig. 7- Philonexis Quoyanus, D'Orb., <? , to show that only seven arms are 

 present, which are not hectocotylized, and that the eighth, which 

 is converted into a Hectocotylus, lies concealed in a sac between 

 the eye and funnel. Magnified three times. 



Fig. 8. Its Hectocotylus more strongly magnified : a, vesicular apical por- 

 tion ; d, flagellum ; e, portions of " branchiae." 



IX. — On the Occurrence of the genus Cryptoceras in Silurian 

 Rocks. By E. J. Chapman, Professor of Mineralogy and 

 Geology in University College, Toronto. 



But one living genus of the chamber-shelled Cephalopods being 

 known, the classification of the numerous fossil types met with 

 more particularly in the Palaeozoic and Secondary rocks, is of 

 necessity based on characters derived immediately from the shell 

 itself. For the purpose of classification, four characters, of more 

 or less value, are especially available. These comprise — (1) the 

 character of the aperture; (2) the form of the septa; (3) the 

 position and character of the siphuncle ; and (4) the form and 

 mode of growth of the shell. 



The aperture may be — {a) open ; {b) contracted. The septa : 

 (fl) simple ; {b) angular or lobed. The position of the siphuncle : 

 (a) central or sub-central ; {b) internal or " ventral f' (c) external 

 or "dorsal.'^ The siphuncle itself: (a) simple; {b) complicated. 

 The form of the shell: (a) straight or conical; (b) arched or 

 " horned'^ in various ways ; (c) discoidal, with or without con- 

 tiguous volutions ; and (d) spiral. 



By means of these characters, all the trustworthy genera of 

 the chambered Cephalopods may be arranged, conveniently at 

 least, if not naturally, in ten sections or families*, as shown in 

 the following tabular view : 



* Many palaeontologists will, no doubt, think an extended subdivision 

 of this kind very unnecessary, and prefer to group these forms in two, or 

 at the most, in three families ; but in adopting this plan, the characters of 



