Maryland Geological Survey 335 



Family PRODUCTIDAE 



Genus CHONETES Fischer de Waldheim> 

 Chonetes may be distinguished from other Lower Devonian bracliiopods 

 by the striate surface and the concavo-convex contour associated with a 

 few tubular spines along the ventral cardinal edge. There are, however, 

 other genera with spines along the posterior edge, and these may be dis- 

 tinguished from Chonetes as follows : Anoplia has a lamellose exterior 

 and apparently no external tubular spines, though it has otherwise the 

 general expression of Chonetes ; Chonostrophia bears to Chonetes the same 

 relation that Strophonella does to Stropheodonta, i. e., the relative con- 

 vexity of the valves is reversed and a section along the medial line would be 

 sigmoid in Chonostrophia and concavo-convex in Chonetes. 



Choxetes subacutiradiatus n. sp. 

 Plate LXl, Fig. IG 



Description. — Shell small, regularly hemispheric, semicircular in out- 

 line, but little wider than long. Greatest width along the hinge-line, 

 which is 6.5 mm., while the length is 4 mm. Surface marked by well- 

 defined rounded plications, which are usually simple, but here and there 

 one bifurcates toward the anterior margin, while on the umbo increase in 

 number takes place by implantation ; from twenty-five to twenty-eight on 

 each valve. In a New York example there are about forty plications. 

 These are crossed by very fine, closely adjoining concentric lines of 

 growth. Toward each extremity the ventral cardinal margin bears one 

 stout, slightly laterally directed tubular spine and two smaller ones on 

 each side of the beak. Dorsal valve and interior unknown. 



The nearest relationship of this species appears to be C. acutiradiatus of 

 the Onondaga. The latter, however, is a far larger and more winged 

 species. In New York it occurs in the New Scotland member at Slinger- 

 lands and Indian Ladder, Albany County. The species is very rare in 

 Maryland. 



' For an extended description, see Hall and Clarke, 1892, Nat. Hist. N. Y., 

 Pal., vol. viii, pt. i, pp. 303-309. 



