THE NAUTILUS. 91 



The writer's first knowletlge of the characters of the two species 

 certainly convinced him that tliey were widely separated, and in 

 order that this fact might be made apparent to others, some fine 

 suites of both forms were shown and commented upon at a recent 

 meeting of the Phila. Acad, of Xat. Sciences, and, it may be added, 

 that the conchologists present fully endorsed the views of the speaker. 



The several prominent characters exhibited by C. fornicata are as 

 follows : 



1st, the lateral curve of the apex, which, though very prominent, 

 is, as a rule, closely attached to the body of the shell. 



2d, the bow-like curve of the free edge of the interior arch. 



3d, the well-defined nick at the junction of the latter w'ith the 

 outer wall of the shell. 4th, the concave form of the septum, which is 

 the same in all stages of growth. 



Other characters might be noted, but those given will doubtless 

 suffice to separate the species, as C. glauca has none of the features 

 alluded to. 



The apex of the latter species is quite small and comparatively 

 free from contact with the body of the shell. It is also horn-like in 

 appearance, usually shining, and but slightly inclined to curve 

 laterally. 



The free edge of the septum is straighter than that of C. fornicata, 

 and the notch is not only absent but I'eplaced by a slight advance 

 of that part of the plate along and against the inner wall of the 

 shell. Another, and perhaps the strongest character of the group is 

 the convex form of the septum. 



This feature, which is a constant one, may be safely depended on 

 to distinguish the species at once from C. fornicata in which the septum 

 is ahvays depressed. The general outline of the shells will also help 

 the student to divide the species, C. fornicata as a rule being pear- 

 shaped, while C. glauca is usually disk or quoit-like in form. The 

 prevailing color of the latter is also a distinguishing mark, the inside 

 of the shells being of a dark brown color and the outside a dai'k gray 

 or purple. 



That a species so well mai'ked as C. glauca should be dropped or 

 merged into another Avithout a given reason, is no small matter, and 

 more than one student will doubtless thank the eminent Doctor for 

 some ex})lanation. 



It may be of interest for some readers of the "Xautilus" to know 

 that a verv fine suite of the shells can be seen in the New Jersev 



