276 NORTH AMERICAN INDEX FOSSILS. 



two divergent grooves.which divide again. Sometimes indications 

 of a few coarse plications present. 

 Niagaran beds of Iowa. 



228^. P. oblongus var. cylindricus Hall & Whitfield. Siluric. 



Elongate, subcircular in cross-section. Valves more or less dis- 

 tinctly trilobed in anterior half, rounded or truncate in front, gen- 

 erally with shallow sinus in each valve in front. Beak of more 

 convex (pedicle) valve overarching. 



Niagaran near Louisville, Kentucky, Wisconsin and Indiana. 



LXVIII. Clorinda Barrande. 



Small, pentameroid. Median sinus in pedicle valve and fold in 

 brachial. Surface smooth or rarely plicate. Spondylium without 

 a supporting septum. Siluric. 



229. C. (Barrandella) f ornicata (Hall). 



(Fig. 335-) Siluric. 



Pedicle valve very convex with over- 

 arching beak. Surface obscurely pli- 

 cate longitudinally. Umbo of pedicle 

 valve much more gibbous than in O 

 ventricosa. 

 Clinton and Niagara of New York, Indiana, Wisconsin. 



230. C. (Barrandella) ventricosa (Hall). (Fig. 336, a-b). 



Siluric. 



Small, subglobose, usually wider than long. Both valves strongly 



ventricose with, incurved beaks, that of the pedicle valve being 



FlG. 335. Clorinda f ornicata 

 (Pal. N. Y.). 



Fig. 336. a-b, Clorinda ven'ricosa. (After Nettelroth.) c, Gypidula comis. 

 (AfterWalcott.) 



much the higher. Surface more or less marked by concentric 

 lines of growth. 



Niagaran of Kentucky, Ohio, Illinois, Wisconsin. 



