No. 2.] 



BILLINGS — PALEOZOIC FOSSILS. 



217 



at first slope backwards from the ventral edge, and then turn 

 upwards and pass over the dorsum at a right angle to the length. 



When the width of the aperture is seven lines, the depth is 

 about five. The operculum has not been identified. 



Collected by T. C. Weston at Bic and St. Simon. 



Genus Obolella, Billings. 

 5 6 7 



.-9 .9: 



Fig. 5. Interior of the ventral valve of 0. gemma, enlarged abont 

 five diameters, acr, the two small scars at the hinge ; bb, the two 

 central scars ; c, the small pit near the hinge ; dd, the two principal 

 muscular scars ; g, the groove in the area. 



6. Interior of the ventral valve of O. desquamata. Hall,* enlarged 

 2J diameters. 



7. Interior of the ventral valve of Oboliis Apollinis, Eichwald, copied 

 from Davidson's " Introduction to the study of the fossil Brachiopoda." 



Generic Characters. — Shell unarticulated, ovate or sub- 

 orbicular, lenticular, smooth, concentrically or radiately striated, 

 sometimes reticulated by both radiate and concentric striae. 

 Ventral valve with a solid beak and a small more or less distinctly 

 grooved area. In the interior of the ventral valve there are two 

 elongated sub-linear or petaloid muscular impressions, which ex- 

 tend from near the hinge line forward, sometimes to points in 

 front of the mid-leno;th of the shell. These are either straii>;ht or 

 curved, parallel with each other or diverging towards the front. 

 Between these, about the middle of the shell, is a pair of small 

 impressions, and close to the hinge line a third pair, likewise 

 small, and often indistinct. There is also, at least in some species, 

 a small pit near the hinge line, into which the groove of the area 

 seems to terminate. In the dorsal valve there are six impressions 



* Engraved from a figure kindly drawn for me by Thos. Davidson, 

 Esq., F.R.S., of Brighton, England. The specimen is from the origi- 

 nal locality of the species, Troy, N.Y. Collected by T. C. Weston 



