576 Systematic Paleoxtology — Tapper Devonian" 



being less transverse, sinus less sharply depressed, nmbo of ventral valve 

 less gibbons, plications less angular, 3-5 plications on sinus, septum and 

 dental lamellae more prominent. While referable to C. congregata they 

 show clear affinities with C. contrada. These two species are so closely 

 connected l)y transitional forms that it appears not improbable that 

 C. (1)11 gr( (/(lid. of the Hamilton may have gi\en rise to C. contraefa of the 

 upper pait of the Chemung rendering the discrimination of the two 

 species insecure at times. This is especially true of individuals occurring 

 in the lower part of the Chemung, some of which might be referred with 

 almost equal propriety to either species. Ty})ical iiulividuals of C. con- 

 tracta appear only in the upper part of the Chemung of ^Maryland so far 

 as observed. 



This variety is one of the most characteristic and abundant forms 

 of the Parkhead fauna, lieing found in certain layers in such profusion as 

 to form a veritable cocjuina, and is one of the most valuable iKuizon uuu k- 

 ers of the Parkhead, with which it is coextensive. It occurs chiefly in the 

 massive sandstones and conglomerates of that member. 



Occurrence. — Jennings Formation, Parkhead Member. Allegany 

 Grove, 800, 850; Williams Eoad, on Polish Mountain, 1289, 13(i2, 1371, 

 1524, KiGO abundant: Xational lioad, on Polish Mountain, 119G, 1G25; 

 section 2 miles north of mouth of Town Creek, 1282 abun(Uint. 1312 abun- 

 dant, 1642 common, 1087 abiandant, 1716, 1723 abundant, 1917; Town 

 Creek, 1605 abundant, 1679 abundant, 1863 abundant; 2 miles west of 

 Pawpaw, West Virginia, 1493 abundant, 1584 abundant, 1712 abundant, 

 1894; Little Orleans, 730 al)un(lant: Fiftcenmile Creek, 1 mile al)0ve 

 Little Orleans, 1713, 1746 abundant, 1766 abundant, 1773 abundant; 

 Tonoloway, 1285 abundant; Hancock, 1600 abundant; Millstone, 1600 

 abundant; Berkeley Springs, West Virginia, 1560 abundant; Yellow 

 Springs, West Virginia, KiOO abundant; 2^,4 miles north of mouth of 

 Sideling Hill Creek, abunchmt; Woodmont. 1285; Xational Road, west of 

 Tonoloway Eidge, abundant. An unusually large form of this \ariety 

 occurs in the Parkhead in the section on Williams Eoad, 4 miles east of 

 Cumberland, 1393 ; road 1 mile north of Rocky Run and 1% miles east 

 of the crest of Knobly ^Mountains. A variety of this form with sinus 



