

NucuLA. 472 



Clinton group, McKee's ore bank, seven miles northwest of 

 Lewistown, Mifflin county, Pennsylvania. (Proc. Am. Phil. 

 Soc. Dec, 1888. Transactions, 1889, Art. YIII, page 451, fig. 

 19.) Founded on specs. 501-48,-51; 502-16; 505-11,-41,-42; 

 from Clinton shales^ over fossil ore ied. Va. 



Nucula tumida^ England. See N. ventricosa. XIIL 



Nucula subtrigona, new species^ Simpson, Proc. Amer- 



^w^ ^^^^-^^ ^^r^^ 3 Phil. Soc. Philada., Dec. 



X'" V- /^w^--^^t. jf^0^MS9^^ 1888, published in Trans- 



'^'"WS9M actions, Art. YIII, p. 451, 

 m^ fig. 1, natural size, fig. 2, 

 APS. Trims^'^^''^^'^'^ ---^=-- ^^^ same shell enlarged 



j5mc6, fig. 3, another, also ente/'^ec? ^mc6/ founded on speci- 

 mens 502-10, -11, -21, in Ashburner and 0. E. HalPs collec- 

 tions, at Orbisonia, Huntingdon Co. ; 0. E. HalPs coll. at 

 Matilda furnace, Mifflin Co.; and 508-15, Hall & Fellows' coll. 

 at Orbisonia, all from Clinton^ Va. Shell somewhat variable 

 in form, usually subtrigonal ; length and height about equal ; 

 basal margin regularly rounded, not constricted toward the 

 posterior end ; posterior margin rounded or obscurely truncate ; 

 anterior margin abruptly rounded ; cardinal line very abruptly 

 declining anterior to the beak, more gradually declining to the 

 posterior. Valves slightly convex, somewhat flattened as they 

 approach the basal margin. Beaks about one-third the length 

 of the shell from the anterior end, not prominent, compressed, 

 extending above the hinge line ; umbonal ridge obscure, very 

 slightly arching upward ; posterior slope very narrow, rounded. 

 Surface marked by fine concentric striae and occasional varices 

 of growth. The concentric striae are often very obscure, the 

 shell appearing essentially smooth. Hinge line, posterior to 

 the beak, marked by a row of fine, transverse teeth. Three 

 specimens, representing the extremes in form, measure respec- 

 tively 10, 4 and 4 mm. in length, and 10, 3 and 2 mm. in height. 

 Larger specimens occur. This species may easily be distin- 

 guished from jY. sinuosa by the absence of a constriction in 

 the basal margin, furrow below the umbonal ridge and striae 

 on the posterior slope. Formation and locality. Chemung 

 group, north of Blackleg creek, Orbisonia, Huntingdon Co., 

 Pennsylvania. 



