CALYMENE. 



55 



Relation of Hypostoma to Cephalon in Calymene. 



In Calymene the shape of the hypostoma bears little relation to the shape of the gla- 

 bella, and it is relatively smaller, both shorter and narrower, than in Ceraurus. In shape, 

 neglecting the side lappets at the front, it is somewhat rectangular, but rounded at the back, 

 where it is bifurcated by a shallow notch. The anterior edge has a narrow flange all 

 across, which is turned at almost right angles to the plane of the appendage, and which 



Fig. 16. Restoration of Calymene senaria Con- 

 rad, based upon data obtained from the study of 

 the translucent sections made by Doctor Walcott. 

 Prepared by Doctor Elvira Wood, under the su- 

 pervision of the author. About twice natural size. 



fits against the doublure of the free cheeks at the sides and against the epistoma in the 

 middle. The side lappets show on their inner (upper) surface shallow pits, one on each 

 lappet, which fit over projections that on the dorsal surface show as deep pits in the bottom 

 of the dorsal furrows in front of the anterior glabellar furrows. The appendifers on 

 the head in Calymene take the form of curving projections of shell underneath the gla- 

 bellar and neck furrows, and owing to the narrowness of the hypostoma, all these are visi- 

 ble from the ventral side, even with it in position. This shield extends back about 0.6 of 



