80 A. K Verrill — The Opisthoteuthidm. 



this group, this can only be regarded as an extreme secondary 

 modification, due to a high degree of specialization connected 

 with the adoption of a creeping and clinging mode of life, 

 analogous to that of the chitons and limpets. It certainly 

 cannot be regarded as a survival of a primitive arche-mollus- 

 can condition. It is not probable that the analogous positions 

 of the organs in the chitons should be considered as arche-mol- 

 luscan, or as proving that such were the original positions of 

 parts in the ancestral forms of all mollusca. The chitons 

 themselves are peculiarly specialized forms of gastropods, 

 adapted to a special mode of life, and therefore cannot be con- 

 sidered as very primitive. Moreover, normal gastropods, so 

 far as known, appeared earlier than chitons in geological time. 

 Chitons are sparingly represented in the Lower Silurian, but 

 normal gastropods are common in the Lower Cambrian, asso- 

 ciated with the earliest forms of life yet known. 



Figure 7. — Loligo Pealei in its natural position, at rest, from life. One-sixth 



natural size. 

 Figure 8. — Octopus Bairdii, young male, at rest, from life; &, hectocotylized arm. 



The real arche-mollusca were far more probably similar to 

 the simpler forms of gastropod and pteropod proveligers and 

 veligers and, like these, free-swimming forms. 



It is probable that many of the early cephalopods, such as 

 Orthoceras and allies, having a long and very unwieldy shell, 

 with a comparatively small last chamber, were not capable of 

 swimming, but were either nearly sessile, and lived with the 

 shell more or less buried in the mud, or else dragged the 

 shell slowly over the bottom. The same was probably true of 

 the irregularly curved forms, both of the JNautilacea and 

 Ammonacea. Such forms would, however, have had active 

 swimming young, perhaps of the veliger type, as a necessity 

 for their wide dispersion. 



The recent discovery^ that Conularia was sessile and at- 

 tached at the apex, renders it probable that the genus belongs 

 to the Cephalopoda, when its other characters are also consid- 

 ered. It is probable, in that case, that it represents a very 

 primitive group, in which the initial secretion of the shell- 

 gland of the veliger-like young served for attachment. As 

 the group cannot be referred to any recognized order or sub- 

 order, it may be designated as Conulariacea. It may, very 

 likely, have been an ancestral form of Dibranchiata. 



* R Ruedemann, Amer. Geologist, vol. xvii, p. 158, March, 1896. 



