284 Mr. Toulmin Smith on the Classification 



5. Cephalites hullatus. PL VII. (vol. xx.) fig. 3, & PI. XIV. 

 figs. 6 & 7. 

 Plaits broad and deep : outer plaits raised in large and very pro- 

 minent projections at considerable intervals, and in such man- 

 ner that they range spirally round the whole body : projections 

 nearly lozenge-shaped and terminating abruptly in an almost 

 flat and somewhat expanded top, having a slight depression from 

 the upper angle towards the middle : inner plaits having large 

 circular depressions at equal intervals ; bulging on each side 

 around depressions till adjoining plaits meet and open into 

 each other : processes very conspicuous : wall very thick. 



This is a most curious and interesting as well as rare but well- 

 marked species. The depressions on the inner folds are much 

 larger than in C. guttatus, which latter have been seen to be 

 larger than in C. longitudinalis. But the external fold is the 

 most deserving of attention. When the specimen is first opened 

 there are seen only a number of nearly semilunar marks. On 

 carefully applying the point of the knife it is found that this se- 

 milunar appearance is caused by very prominent projections, the 

 tops of which are all closed, but have a partial depression at their 

 upper extremity, and which depression is filled as usual with the 

 matrix. The projections themselves are of large size, measuring 

 about two lines in their longest diameter. They stand out nearly 

 or quite half the thickness of the wall, which is generally four 

 lines thick (see fig. 3. PI. VII.*). They diff'er widely from any- 

 thing we have yet seen. Instead, like Ventriculites mammillaris, 

 of being mere rounded elevations on the plait, they stand out 

 prominently from it ; and a careful dissection shows that their 

 shape is generally that of a lozenge, with the acute angles in the 

 horizontal, and the obtuse in the perpendicular, line of the whole 

 body. Fig. 7t of PI. XIV. shows the manner of the projections 

 from the plait and the figure which the peculiar shape of their 

 tops causes to be seen on a clean section exactly through the 

 middle of any one. In all the specimens of this species which I 

 have seen, the projections run in nearly regular spiral lines round 

 the body. 



On the inner surface of this and of some other broadly de- 

 pressed species there is a very small and slight depression be- 

 tween each of the large depressions, and both on the plaits and 

 on the places of the united bulgings. It is barely traceable, and 



* This is a longitudinal section taken rather obliquely in order to preserve 

 the roots. It is not quite regular therefore; but, on the side which is pre- 

 served, the projections can be well distinguished. 



t In this figure I have connected the inner and outer plaits by brackets, 

 .^the outline of each merely being given for the sake of clearness. 



