342 Systematic Paleontology 



CHONOSTROniiA HELDERBERGiA Hall and Clarke 

 Plate LXII, Fig. 3 



Chonostrophia helderbergia Hall and Clarke, 1892, Pal. N. Y., vol. viii, pt. i, 

 p. 353, pi. XV&, fig. 14. 



Description. — Shell large, semicircular, very slightly concavo-convex, 

 being nearly flat, slightly resupinate, greatest v^idth at hinge-line. Ven- 

 tral valve slightly convex, umbo scarcely concave, concave towards cardinal 

 extremities. Area low. Dorsal valve slightly concave, umbo scarcely 

 convex. Surface ornamented by fine equal thread-like stria? and crossed 

 by fine concentric lines. A single very strong elevated rib extends from 

 umbo nearly to front of valve. Cardinal margin bearing about 7 spines 

 directed obliquely outward, spines near iimbo very small, becoming 

 stronger towards extremities. 



Length 1.7 cm. ; width 2.8 cm. 



This fine and striking shell is distinguished from all other species 

 of the fauna by its strong median rib. It becomes abundant locally at the 

 base of the New Scotland limestone. 



Occurrence. — Helderberg Formation, New Scotland Member. 

 Dawson, Devil's Backbone. 



Collection. — Maryland Geological Survey. 



[Swartz.] 



Superfamily PENTAMERACEA 

 Family PENTAMERID/E 



Genus GYPIDULA Hall 



Gypidula (Sieberella) coeymanensis n. name 



Plate LXII, Figs. 4-7 



Atrypa galeata Vanuxem, 1842 (not Dalman), Geol. N. Y., Rept. Third Dlst., 



p. 117, fig. 1. 

 Atrypa galeata Castelnau, 1843, Essal Syst. Sil. I'Amer. Septent., p. 39, pi. xiv, 



fig. 4. 

 Pentamerus galeatus Hall, 1857 (not Dalman), Tenth Ann. Rept. N. Y. State 



Cab. Nat. Hist., p. 105, figs. 1-3. 

 Pentamerus galeatus Rogers, 1858, Geol. Penn., vol. ii, pt. ii, p. 825, fig. 646. 



