MOLLUSCA. 7 



inferred. 1 M. de Blainville 2 has demonstrated some of the chief characteristics of the 

 dibranchiate type of structure from which the decapodous character of the head (wanting in his 

 specimen') might be deduced, and thus concomitant inferential proof be had of the accuracy ; 

 before doubted, of Lamarck's figure. Finally Mr. Cuming's specimen, described and figured 

 by Mr. Gray 3 and Mr. Lovell Reeve,* sets at rest the question of the external decapodous 

 characters of Spirula, and confirms M. de Blainville's description of the terminal appendages 

 of the mantle and the position and degree of exposure of the shell, at least in certain speci- 

 mens of Spirula. It needed but the examination of the internal structure of Mr. Cuming's 

 specimen to prove the accuracy of the inference of the dibranchiate type of internal organiza- 

 tion from the decapodous external structure of the animal, and reciprocally. 



Another point also remained for consideration, viz., whether the figure by Peron (pi. iv. 

 fig. 1 *), showing a comparative shortness of the mantle in proportion to its breadth, and the 

 absence of the terminal disc and fin-like appendages, truly indicated such a form of Spirula 

 in nature ? Or, whether the continuous exposure of so large a portion of the outer whorl of 

 the shell, as is represented by Peron, might not be due to accidental laceration of the disc 

 and appendages from the rest of the mantle ? And whether, if such differences were natural, 

 they were differences of age, or sex, or species ? Towards the solution of these questions, and 

 the completion of the anatomy of the Spirula, the facts which I have now to offer, though 

 not of much importance, may contribute : they are the result of careful and, I trust, faithful 

 observation, and every little will be welcome to the genuine student of nature in a question 

 of so much diffi culty and interest as the present. 



The specimen of Spirula (pi. iv. fig. 1, 4, 5, 6) which Capt. Sir Edward Belcher was so 

 obliging as to place in my hands for description and dissection, like that of M. de Blainville, 

 had the head and its appendages torn away ; but the infundibulum (c) was left, with the 

 mantle and shell (ch). The shell, partly imbedded in the hinder end of the mantle, had the 

 greater part of the last whorl uninterruptedly exposed (fig. 7), and the thick borders of the 

 terminal lobes of the mantle (dd, fig .4, 7, and 11) which extended over the umbilicus and inner 

 whorls of the shell, were smooth, rounded, and entire. The exposed part of the shell was 

 coated by a thin epiderm : the last whorl was directed from the ventral to the dorsal aspect, 

 bending round the end of the body, and advancing forwards, not again entering the mantle, 

 but with the last or open chamber, terminating freely over a small opening of the mantle 

 (fig. 6,fn) through which the membranous siphon of the shell (sA) passed, and from which 

 opening part of the second whorl of the shell protruded. The proportions of the body, or 

 mouth, especially its shortness as contrasted with its dorso-ventral diameter, accord with those 

 of Peron's specimen (op. cit. and fig. 1 *) : as does also the exposed position of the last 

 whorl of the shell, concomitant upon the absence of the terminal fleshy disc and its appendages. 



1 Owen, Memoir on the Pearly Nautilus, p. 54, and Classification of Cephalopods, Zool. Trans, v.ii. pp. 123, 129. 



2 Loc. cit. 3 Annals of Natural History, vol. xv. p. 257. pi. XV. 



4 Elements of Conehology, p. 16. pi. A. 



