Maryland Geological Survey 601 



Occurrence. — Jennings Formation, Chemung Member. Near Penn- 

 sylvania-Marylaud line west of Green Kidge in upper Tropidoleptus hori- 

 zon ?. Parkhead Member. Two miles north of mouth of Town Creek, 

 1842 ?, 1949 ?; 2 miles west of Pawpaw, 1612 ?. Woodmont Member, 

 Ithaca Fauna. Two miles west of Pawpaw, 1340 abundant; Little 

 Orleans, 144G; Fifteenmile Creek, 1 mile above Little Orleans, 1446; 

 Woodmont, ;iO, 776, 1024, 1033 abundant, 10G7, 1285; National Road 

 west of Tonoloway Eidge; Hancock 690, 935, 994 ?, 1149 abundant, 

 1274 abundant, 1149 to 1274 abundant; Hancock-IIarrisonville Eoad, 

 726, 880 abundant, 944; Millstone 1057, 1122, 1141, 1148; Berkeley 

 Springs, West Virginia, 712, 755, 1010, 1058, 1074, 1080 abundant, 1163, 

 1371 abundant ; Yellow Springs, West Virginia, 629, 665, 734 abundant. 



Collection. — Maryland Geological Survey. 



Spirifer (Delthyris) mesacostalis Hall 

 Plate LVIII, Figs. 11-23; Plate LIX, Figs. 1, 2 



Spirifer mesacostalis Hall, 1867, Paleontology of New York, vol. iv, p. 240, 



pi. xl, flgs. 1-13. 

 Spirifer mesacostalis Grabau and Shimer, 1909, N. Amer. Index Foss., vol. i, 



p. 332, fig. 424a. 



Description.' — This species resembles S. mucronaius externally but dif- 

 fers in possessing a distinct median septum in the ventral valve. While 

 the cardinal angles are ordinarily simply acute in some cases the extremi- 

 ties are greatly extended, increasing the resemblance of the species to 

 S. mucronatiis. The presence of a median septum in the interior, how- 

 ever, affords a distinct criterion for the separation of the two forms. This 

 species is exceedingly abundant in the Parkhead and continues common 

 to the upper conglomerate of the Chemung, above which it is less frequent. 



Length 15-20 mm. ; width 30-40 mm. 



Occurrence. — Jennings FoiaiATiox, Chemung Member. National 

 Eoad west of Frostburg; Oakland-Altamont Eoad; Oakland-Eedhouse 

 Eoad; Trout Eun section; Allegany Grove, 1153 ?, 1250 abundant ?, 

 1310 abundant, 1520, 2020, 2111, 2340; Ellerslie, Pennsylvania, 1316 

 abundant, 1474; Williams Eoad, on Polish Mountain, 2382 abundant. 



