152 Annals of the Carnegie Museum, 



of the Birmingham shale at the eastern end of the second cut on the 

 Pennsylvania Railroad east of Summerhill, Pa. 



Family ATHYRID^ Phillips. 



Genus Composita Brown. 



Composita girtyi sp. nov. 



Plate XXVIII, figures i-ii. 



Shell small, almost globose, with a slight fold on the brachial and flat 

 sinus in the pedicle valve. There is considerable variation in the outline 

 of these shells as viewed from above the brachial valve, and in the strength 

 of the fold and sinus. In some the outline is almost circular, while in 

 others it is oval, as the shells are sometimes longer than wide. The sinus 

 of some specimens is merely a flattening of the ventral valve toward the 

 front, while in others the sinus is a narrow groove extending almost to the 

 beak. A single specimen which probably belongs to this species has a 

 narrow sinus in both valves, like Composita emarginata Girty from the 

 Permian of Texas. This is, however, the only specimen seen which shows 

 any trace of a sinus in the brachial valve, and may represent another 

 species. The surface is smooth except for the strong, rather distant 

 lines of growth. The entire interior has not been seen, but weathered 

 specimens show rather closely coiled spiral brachidia. 



This shell is much smaller that Composita subtilita (Hall) and is readily 

 distinguished from the young of that species by its globose form and the 

 contour of the front of the shell. It is more closely allied to Composita 

 mexicana (Hall), but the fold and sinus are not so strongly delimited as in 

 that species. 



A large specimen is li mm. long, lo mm. wide, and 9 mm. in thickness. 

 One of the narrow shells is 10 mm. long, 8 mm. wide, and 9 mm. thick. 

 A less tumid shell is 10.5 mm. long, 10 mm. wide, and 7 mm. thick. The 

 majority of the shells have about the proportions of the first of these. 



Locality. — This is one of the most common shells in the Vanport lime- 

 stone in western Pennsylvania. It has been found at Wampum, New 

 Castle, and Kittanning. The cotypes are from the abandoned quarry 

 between New Castle and New Castle Junction. In this quarry the shell 

 is especially abundant, over 1,200 specimens having been picked up there. 

 The species is named for Dr. George H. Girty, whose studies have so greatly 

 extended our knowledge of the invertebrate faunas of the Carboniferous 

 and Permian. 



