Maryland Geological Survey 339 



while in the smaller or younger spoeiinoiis the ribs may be straight or in 

 others have the peculiar curvature. 



Occurrence. — Helderberg Formation, Key"ser Member. Dawson, 

 Cookerly, Cash Valley, Devil's Backbone, Breakneck Hill, Plintstone, \\ 

 miles east of Eush, Hancock, Tonoloway, Maryland; Keyser, West 

 Virginia. 



Collection. — Maryland Geological Survey. 



[Maynard.] 



Chonetes jerseyensis var. spinosus n. var. 

 Plate LXI, Fig. 20 



Descriplion. — This variety of Chonetes jerseyensis differs in being 

 larger and having a greater number of marginal spines on each side of 

 the beak. Pedicle valve slightly more convex. The radiating ribs are 

 coarser and somewhat nodose. 



Length 17 mm. ; width 22 mm. 



Occurrence. — Helderberg Formation, Keyser Member. Hancock. 



Collection. — Maryland Geological Survey. 



[Maynard.] 



Genus ANOPLIA Hall and Clarke' 

 The shells referred to Anoplia are small, smooth or slightly lamellose 

 chonetoids, with the muscular scars of the ventral valve not elongate and 

 divided by a very short, high, and bluntly terminating median septum. 

 In A. helderhergice the tubular canals in the thickened ventral cardinal 

 area pass through the shelly matter and terminate in spines, as in 

 Chonetes. In A. nucleata the spines have not been seen and it may be 

 that we have here an atavistic tendency to a non-spinose condition. While 

 the absence of spines was taken to be the chief distinguishing character 

 separating Anoplia from Chonetes, still the genus is a good one and 

 will embrace the early smooth or slightly lamellose, highly convex, small 

 chonetoids with a ventral median septum. The smooth forms of Chonetes 

 are not the descendants of Anoplia, but are derived from associated finely 

 striated forms of the former genus. 



' See Hall and Clarke, 1892, Nat. Hist. N. Y., Pal., vol. viii, pt. i, p. 309. 



