75 



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, 

 and furnishes another characteristic by which it may be at once 

 known from V. mammillaris. 



3. Cephalites paradoxus. PI. XIV. fig. 3. 



Plaits narrow but deep : outer plaits depressed irregularly ; 

 bulging around depressions till the adjoining plaits meet and 

 open into each other : inner plaits regular and simple : pro- 

 'cesses conspicuous : wall thick. 



I have given to this remarkable species the name paradoxus, 

 because it differs from every other species of this genus in having 

 the plaits simple and regular on the inside, while all the com- 

 plexity is on the outside. 



The depressions, and consequently the interspaces between the 

 anastomosing bulgings on the outside, are not of a regular figure, 

 as is the case on the inner surfaces of Ventriculites radiatus and 

 other species. They are varying and elongated; often almost 

 angular ; though, as the plaits are narrow, never very large. There 

 do not appear to be any points of anastomosis* between the ad- 

 joining inner and regular plaits, such as are found between the 

 outer plaits of V. radiatus. 



4. Cephalites alternans. PI. VII. fig. 2, & PI. XIV. figs. 4 & 5. 



Plaits rather broad and very deep : both outer and inner plaits 

 depressed at unequal intervals ; bulging on each side around 



* The appearances seen on dissecting away the inner surface must not 

 be mistaken for this anastomosis. They are, in fact, the bases of the de- 

 pressions on the outer plaits. See the description of a similar appearance 

 on the outside of V . lenuiplicatus, p. 68. 



