MARYLAND GEOLOGICAL SURVEY 363 



Superorder OSTRACODA 

 Family LEPERDITIIDAE 



Genus ISOGHILIXA Jones 

 ISOCHILINA GREGARIA (Whitfield) 



Plate XXXVI, Figs. 10-12 



Primitia gregaria Whitfield, 1889, Bull. Amer. Mus. Nat. Hist., vol. ii, p. 58, 



pi. xiii, figs. 3-5. 

 Isochilina gregaria Jones, 1890, Quart. Jour. Geol. Soc. London, vol. xlvi, 



p. 22, pi. i, figs. 9, 10. 

 Isochilina amiana' Ulrich, 1891, Jour. Cincinnati Soc. Nat. Hist., vol. xiii, 



pt. 1, p. 180, pi. xi, figs. 12a-c. 

 Isochilina Ottawa var. intermedia Jones, 1891, Cont. Micro-Pal., Geol. Surv. 



Canada, pt. 3, p. 66, pi. x, figs. 10, 11. 



Description. Carapace about 4 mm. long, obliquely oval in form; 

 hinge line straight, in length about three-fifths that of the valves. Sur- 

 face of valves convex, most elevated across the narrow end. Sulcus 

 poorly defined, broadly triangular extending from about the middle of the 

 valve to the hinge. Surface of valves marked by numerous widely spaced 

 pits. On each side of the sulcus there is usually a well-defined node or 

 tubercle and often one is at its lower extremity. 



A species of similar size and shape and with the surface markings of 

 the Vermont type specimens occurs in poor preservation, but sometimes 

 in abundance on the weathered limestone surfaces of the Middle Beek- 

 mantown of Pennsylvania and Maryland. 



Occurrence. BEEKMANTOWST LIMESTONE (Ceratopea zone). Several 

 of the outcrops along the National Highway west of Hagerstown and the 

 turnpike to Williamsport, Maryland. 



Collections. Maryland Geological Survey, U. S. National Museum. 



ISOCHILINA SEEYLI (Whitfield) 

 Plate XXXV, Fig. 12 



Primitia seelyi Whitfield, 1889, Bull. Amer. Nat. Hist, vol. ii, p. 60, pi. xiii, 



figs. 6, 7. 

 Isochilina seelyi Jones, 1890, Quart. Jour. Geol. Soc. London, vol. xlvi, 



p. 22, pi. i, fig. 7. 



