CEPHALOPODA. 419 



the space of 60, 110 and 125 ram. respectively. Siphuncle large, subcen- 

 tral, slightly expanding between the septa ; its elements not fully observed. 

 The ventral side of the shell is indicated by a sharp, narrow, longitudinal, 

 raised line on the outer face of the chambers, on the convex side of the 

 volution. 



.Test preserved only in a macerated and exsolute condition. Surface 

 marked by fine and coarser, irregular, lamellose lines of growth, and fine, 

 regular, undulating, elevated, thread-like strife, parallel to the lines of 

 growth ; longitudinally marked by rounded, or sometimes sharper, undulat- 

 ing, revolving strife, of which there are five or six in the space of five mm. 

 These markings are visible on the cast, or on the macerated inner laminae of 

 the shell. 



The internal cast is strongly marked by the suture lines, which are deeply 

 impressed from the solution and removal of the imbricating margins of the 

 septa ; and the filling of these narrow spaces is usually more or less broken, 

 leaving the suture lines irregular. In all the specimens the surface of the 

 cast or of adhering inner portions of the shell is pitted with minute, rounded 

 depressions, or with corresponding elevations, which appear to be of organic 

 origin. This marking pertains to the inner layer of the shell, or to the 

 immediate underlying or interior surface, and bears a close resemblance to 

 the markings of the organic deposit in Orthoceras luxum. 



The largest known specimen of this species has a diameter of 360 mm. ; 

 and the chamber of habitation of the same specimen, measured along the 

 middle of the lateral face, has a length of more than 360 mm., and measured 

 on the periphery, has a length of more than 450 mm. 



In nearly all the specimens observed the chamber of habitation is more or 

 less covered with scattered groups of a parasitic Bryozoan, having the form 

 of a low, flat disc, with a central depression. These discs have a diameter of 

 from six to fifteen mm., and the only structure exhibited is a radiate and 

 concentric arrangement of obscure pores or cells. There is also frequently a 

 tubular, branching Bryozoan upon the surface of the cast, which appears to 

 have been attached to the interior of the shell. 



