119 



opercula, and that their internal structure was materially different from 



that of anv orthoceratices which had been hitherto described *. 



it 



These shells, Plate VIII. Fig. 1 and 5, undoubtedly require to be 

 considered as of a distinct genus from orthoceratites. Like orthoceratites, 

 they are fossil, testaceous, conical tubes, more or less approaching to a 

 cylindrical form, being sometimes straight and sometimes curved, and 

 internally divided into numerous chambers by horizontal septa : but, 

 unlike the orthoceratites, they do not appear to be provided with a 

 syphon ; the functions of this part having been perhaps performed by 

 two converging ridges, which, at no great distance from each other, 

 proceed from the sides of the cavity along its whole length. Soon after 

 their origin, these ridges suddenly contract ; and then, gradually be- 

 coming more tumid, terminate in rounded edges, at about a third of an 

 inch from the sides. The gutter which is formed between these ridges 

 is generally, like the rest of the cavity, divided into chambers by nume- 

 rous transverse septa. Picot describes what he conceives to be the 

 remains of a siphunculus, in two specimens; but the appearances do 

 not appear to be such as to warrant the supposition. The representa- 

 tion of this specimen is, however, here copied from Plate II. Fig. 2, of 

 Picot's work ; Plate VIII. Fig. 5, a, marking the part in which the 

 siphunculus is supposed to have existed. 



The Baron Picot observes, that in several specimens the gutter, 

 or space between the ridges, is entirely empty, or free from septa; but 

 very properly remarks, that this must not be relied on as a specific 

 distinction; since it is probable, that in its original state, it was furnished 

 wiih septa. Having very fortunately obtained some specimens of this 

 curious and interesting fossil, and having amongst them two specimens, 

 in which this part was thus empty, I carefully examined them, and was 

 surprised at not finding the least trace of the adhesions of septa on its 



* Philippi Picot de la Peirouse cle novis quibu&dam OrthoceratUum, &c. Disscvta- 

 tiuncvila. Page 4. 



