212 PSEUDOCERATITES OF THE CRETACEOUS. 
although perhaps older, siphonal saddle has numerous denticles or marginal 
saddles. The median marginal lobe was not quite so plain as in Whitfield’s 
figure, but this might have been owing to age or variation in sutures or the 
condition of the cast. Meek, as well as Whitfield, included under placenta 
several species which are separated in these descriptions, but Whitfield 
recognized and described the differences between the western and the New 
Jersey specimens and considered them as probably distinct. I have 
consequently named the western species whitfieldi in recognition of this 
fact. 
The specimen described above enables me to add the following: The 
venter is not rounded on the smaller end of this cast, but flat, having the 
same form as whitfieldi, but broader than in that species; subsequently, 
although not well preserved, this part appears to become rounded. This 
specimen shows that in extreme age the volution is shorter and has more 
gibbous sides than in whitfieldi and shorter ventro-dorsal diameters. The 
decrease in involution due to senility is also more marked, and takes place 
at a smaller size. This species stands between syrtale and whitfieldi in 
this respect and in its sutures and other characters. 
There are several fragments in the Hale collection of the Boston 
Society of Natural History, supposed to be from Greene County, Alabama, 
which have saddles with more solid bodies or basal parts, as in true 
placenta hese indicate a species of larger size than the associated species 
of P. syrtale, having volutions with smooth flat sides and smooth venter, 
as in placenta. The sutures agree very closely with those given by 
Morton for P. placenta trom the cut of the Delaware and Chesapeake Canal, 
and one specimen shows a rounded venter. The examination of the fine 
suite of original types and specimens in the Museum of the Academy of 
Sciences of Philadelphia gave the following results: The septum of this 
species is much flatter, having only a very slight double curvature im place 
of the very marked double curvature of whitfieldi, and this is less apparent 
on the suture line than on the surface of the septum. On a volution 63 
mm, from line of involution to venter, transverse diameter is 22 mm. and 
there are three lines of tubercles. The lateral row is two-thirds of the 
breadth of the sides, nearer the venter than the dorsum, and very small 
and widely separated, but still quite distinct. The tubercles on the venter 
of placenta are large and elongated like those of bolli and much coarser and 
