292 Mr. Toulmin Smith on the Classification 



the campanulate envelope, to which the projecting points of the 

 plaits were affixed, securing it without. The size of the internal 

 cavity varies in different specimens, as will be seen by figs. 12 

 and 13 of PI. XIV. ; of which fig. 12 is a general view of the 

 external aspect of one specimen ; fig. 13 is a section, with the 

 matrix cleared away from the inner funnel-shaped simple mem- 

 brane, of another. 



There is certainly no form among the Ventriculidse which 

 might, at first sight, be less supposed than the present to have 

 had any affinity with the fossils which have been described as 

 belonging to the genus Ventriculites. This will be well under- 

 stood by comparing PI. XIV. figs. 12 and 13 with any of the 

 figures on PI. XIII. 



The condition in which these specimens are found, — their deep 

 folds preventing their ever coming free from the chalk, or being 

 developed without the laborious use of the needle, — renders it 

 impossible to make any confident observations upon them as to 

 the processes ; a remark which also applies to every other species 

 of the present section. 



3. Cephalites constrictus. PI. XV. fig. 1. 



"Whole body very low, much-elongated and narrow, with roots at 

 one end : plaits very deep, and running longitudinally from the 

 root extremity; each plait constricted at short and not very 

 regular intervals, and sometimes to nearly its whole depth : 

 cephalic membrane covering the whole upper surface and sides, 

 to the margins of which last, as well as to many of the pro- 

 minent points of the plaits, it is attached ; usually constricted 

 at considerable intervals, with a single opening in the middle 

 of each compartment thus caused. 



The specific description will satisfy the inquirer that this is a 

 very extraordinary form. Externally it has nothing which would 

 indicate any Ventriculitic affinity, and it has indeed been described 

 by Dr. Mantell under the name of Choanites subrotundus ; but it 

 has no relation whatever to Choanites. The appearance of the 

 fossils is so remarkable, that, but for the fixed rule of preserving 

 every fragment which I could not understand, I should never 

 have been able to establish or even suspect the true affinities. 

 A suite of seventeen specimens enables me, however, now to point 

 out the true general characters of the species without leaving 

 any room even for doubt. 



In the two very difierent states in which the fossil, or frag- 

 ments of it, are found, it has very different appearances ; the one 

 state (see left hand of figure) shows the upper, the other (see 

 right hand of figui-e) the lower part only, or its cast. The com- 



