62 CONTRIBUTIONS 
lanceolate, excavated, escutcheon long and excavated ; 
nymph small and deeply seated; teeth small; anterior 
and posterior cicatrices placed on a raised seat ; palleal 
cicatrix passing between the two great cicatrices in a gen- 
tle curve ; margin crenulate. 
Diam. .4, Length .7, Breadth .9, of an inch. 
Observations. This interesting and remarkable species 
cannot easily be confounded with any other with which I 
am acquainted, except that which follows. Its oval form, 
flat beaks and large transverse folds or ribs, are remark- 
able. 
In dedicating it to my friend, P. H. Nicklin, Ihave 
great pleasure in acknowledging my obligations to him, 
for his kind assistance in occasional difficult points. 
4. sulcata. Plate 2. Fig. 36. 
Description. 'This species is so precisely similar to the 
last, with the exception of a marginal furrow, that I 
have thought it unnecessary to recapitulate the descrip- 
tion. The Nicklinii is beautifully crenulate on the margin, 
while the sulcata is furnished with a margin, along whose 
inner edge a perfect furrow passes from the anterior to the 
posterior part of the hinge. When very young the speci- 
mens are almost perfectly flat, and might, for this reason, 
easily be taken for a different species. 
