282 Mr. Toulmin Smith on the Classification 



that a section of the entire body presents an a ,g " ' a 

 outline as in fig. F, in which a — b is the sec- 

 tion of the head. The outline of the head 

 is always quite as sharp and well-defined as 

 in this figure. The relative arrangement 

 and proportions of the head and the plaits 

 are such that specimens of this division can 

 never be confounded with any belonging to 

 the section Dilatati. It is very rarely in the 

 present division that there is any rounding, 

 or departure from the nearly flat character of 

 the head; a character, on the other hand, 

 never present in the Dilatati. 



It is proper to notice that, in every species of this genus, in 

 order to give full strength to the head, the depressions, bulgings, 

 and other modifications of the fold, — where it does not rise, as 

 in C. campanulatus, in a simple form, — are so arranged that the 

 membrane of the inner wall, where it adjoins the head, is always, 

 and that of the outer wall most frequently, expanded by a lateral 

 bulging of the plait, so as for the adjoining plaits to meet just 

 at the point of union of the wall with the head. Thus the 

 whole of the inner, and often of the outer, edge of the head is 

 continuously attached to the wall, an arrangement of much im- 

 portance. On this inner edge the membrane often rises up in a 

 narrow and slightly prominent ridge above the otherwise smooth 

 surface of the head. 



2. Cephalites guttatus. PI. XIV. fig. 2. 



Plaits broad and deep : outer plaits raised in large hollow bosses, 

 often elongated ; adjoining plaits having an occasional lateral 

 connection : inner plaits depressed at regular intervals, bulging 

 on each side around depressions till adjoining plaits meet and 

 open into each other : processes very conspicuous : wall usu- 

 ally thick. 



Nothing can better express the usual character of this species 

 than the term guttatus. The outer surface looks exactly as if 

 sprinkled with drops of a viscid fluid which had just begun to 

 run together, in some instances to a greater, in others to a less 

 extent. It is thus generally well distinguishable, even on the 

 outside, from Ventriculites mammillaris. The plaits being much 

 broader than in C. longitudinalis, the depressions on the inner 

 plaits are larger than in that species. 



The lateral connection between adjoining external plaits, as in 

 Ventriculites latiplicatus and radiatus, which is only rarely seen 

 in C. longitudinalis, is always more or less present in this species, 



