18 PPP. HKPOKT OF PROGRESS. C. E. KEECHER. 



wliich. :ilthouc:li not found attaclied to a carapace, is 

 referred to this species on account of the similarity in sur- 

 face ornamentation and from its association with specimens 

 of the carapace of tliis species. 



Formation and locality. In shales at the base of the 

 Chemung group, as exposed at Warren, Pa. 



Tropidocaris ixterrupta, n. sp. 



Plate II, Fig. 6. 



Carapace semi-oval in outline, obliquely truncated be- 

 hind, slightly mucronate in front. Dorsal line straight, 

 somewhat shorter than the greatest length of the valves. 

 Yalves regularly convex, widest in the middle, length more 

 than twice the greatest breadth. Lower and anterior mar- 

 gins regularlj^ curving to the lower posterior end of the 

 valve, which is abruptly rounded, and from whence the 

 margin is concave to the extremity of the hinge. 



Cephalic area marked by a slightly greater convexity 

 than the remainder of the valve, and showing two or three 

 obscure rounded elevations. Optic spots indicated by a 

 swelling or tubercle on one of the short ridges extending 

 from the. apex of the valves. Valves ornamented with three 

 strong ridges which extend the entire length, and by three 

 or four similar ridges extending more than one half the 

 length of the valves. Also on the cephalic region there are 

 from four to five smaller carinse which extend less than 

 half the length of the valve. Abdomen, telson and append- 

 ages unknown. 



Test thin, slightly thickened around the margins of the 

 valves. 



The right valve described has a greatest length of 23 mm., 

 a width across the middle of about 10 mm., and the dorsal 

 line measures 21 mm. 



The carapace of this species somewhat resembles that of 

 T. alterno.ta, but in that species the ridges regularly alter- 

 nate in size and the stronger ones are ornamented with a 

 double series of minute pits along their summits. The 

 greater number of carinse on the valves readily distinguishes 

 it from T. bicarinata. 



