Maryland Geological Survey 347 



which is only conspicuous from the center of the valve to the front, and a 

 single plication on the brachial valve marks the center of an undefined 

 sinus, bordered by two inconspicuous plications near the front. The shell 

 is smooth on both valves from the center posteriorly. The slope from 

 the umbonal regions is abrupt towards the posterior and the posterior 

 region becomes concave ; the lateral margins rounded. The shell is marked 

 by faint concentric lines of growth. Dimensions of an average individual : 

 Length 12 mm. ; width 13 mm. 



This species is distinguished from Gypidula corriganensis by its some- 

 what more globose character, the almost equal convexity of the valves, and 

 by the prominent beaks which are almost equal and directly opposite each 

 other, and by the abrupt slope from the umbonal region to the posterior. 



Occurrence. — Helderberg Formation, Iveyser Member. Cash Valley. 



Collection. — U. S. National Museum. 



[Maynard.] 



Order TELOTREMATA 



Superfamily RHYNCHONELLACEA 

 Family RHYNCHONELLID/E 



Genus RHYNCHOTRETA HalP 



Ehynohotreta cumberlandica n. sp. 



Plate LXII, Figs. 23, 24 



Description. — Shell trigonal or subpentagonal with the posterior sides 

 angulated and nearly vertical; width somewhat greater than the length. 

 Ventral valve flatter than the dorsal, Avith a shallower sinus having two 

 or more often three plications ; beak nearly erect, but not greatly elevated. 

 Dorsal valve deeper than the ventral, but not gibbous, with a depressed flat 

 fold having usually four plications. On each side of the fold and sinus 

 there are commonly four, sometimes five, plications. All the plications 

 are sharply elevated, with subangulated crests. Interior unknown, and 

 also the finer surface markings. 



^For generic description, see Hall and Clarke, 1893, Nat. Hist. N. Y., Pal., 

 vol. viii, pt. ii, p. 185. 



