14 ' North American Palaeozoic Crustacea. 



suhcylindrica, Emmons, 1855; Am. Geology, vol. 1, p. 220, fig. 75 b. 

 Trenton. Pre-occupied by Minister ; change to C. Emmonsi. 



subelliptica, Emmons, 1855; Am. Geology, vol. 1, p. 220, fig. 75 a. 



Trenton. 

 Cytherellina, Jones & Holl, 1869 ; Annals & Mag. Nat. Hist. 4th series, 

 Loudon, vol. 3, p. 215. 



Diucjnosis. — Carapace valves elongate, convex, smooth, thick, excavated 

 internally with undulating contours. 



grandella, Whitfield, 1882 ; Bull. Am. Mus. Nat. Hist. New York, vol. 1, 

 p. 94, pi. 9, figs. 28, 29. Warsaw. 



Cytheropsis, McCoy, 1855 ; Synopsis Classification Brit. Pal. Rocks, pi. 1 L, 

 fig. 2. No definite description of the genus given. 



concinna, Jones ; see Primitia concinna. 



rngosa, Jones ; see Primitia nigosa. 



siliqua, Jones, 1858 ; Annals & Mag. Nat. Hist. 2d series, London, vol. 1, 

 p. 249, pi. 10, fig. 6. Trenton. 



siliqua, Jones, 1858; Geol. Canada, Dec. 3, p. 99. 



siliqua, Jones, 1869 ; Annals & Mag. Nat. Hist. 4th series, London, vol. 3, 

 p. 216, pi. 14, figs. 1, 2, 3, 4, 5, 6. 

 Dipeltis, Packard, 1885 ; Am. Naturalist, vol. 19, p. 293. 



Gen. Char. — "The body is suborbicular, flattened, disk-like, sloping regu- 

 larly and gradually from the median area to the edge ; it is divided 

 into two portions ; the larger one the cephalic shield, and the other as 

 the abdomen. The edge of the body is very slightly emarginate. Tlie 

 integument is rather thin, without segments ; its surface may have had 

 a few scattered small tubercles. The surface is smooth and shining." 



diplodiscus, Packard, 1885 ; Am. Naturalist, vol. 19, p. 293. 



Carboniferous. 



diplodisciis, Packard, 1886; Mem. Natl. Acad. Sci., vol. 3, p. 145, pi. 5, 

 figs. 2, 2 a. 

 DiplostyluB, Salter ; Quart. Jour. Geol. Soc. London, vol. 19, p. 76. 



Gen. Char. — "Carapace unknown. Body-segments (in number ?) arched 

 and with minute pleur?e. Tail-segment large triangular, spinose, with 

 two pairs of simple, ovate appendages." (Salter, Quart. Jour. Geol. 

 Soc, vol. 19, p. 76.) Type C. Dawsoni, Salter. 



Dawsoni, Salter, 1863 ; Quart. Jour. Geol. Soc. London, vol. 19, p. 77, fig. 6. 



Coal Measures. 

 Dipterocaris, Clarke, 1883 ; Am. Jour. Sci., 3d series, vol. 25, p. 121. 



Diagnosis. — Carapace in one piece, ovate in general outline ; normally 

 with an elevated dorsum and sloping sides. Each extremity is strongly 

 notched, dividing the carapace into two broad al.-p connected by a nar- 

 row isthmus, wliich shows no evidence of a dorsal suture or anchylosis. 

 Surface ornamented by concentric elevated lines or wrinkles. (Clarke, 

 I'al. New York, vol. 7, p.-lix.) 



pennre-dsedali, Clarke, 1883; Am. Jour. Sci., 3d series, vol. 25, p. 122, 

 fig. 1. I Chemung. 



pennae-daedali, Jones & Woodward, 1884 ; Geol. Mag., Dec. 3, vol. 1, p. 349. 



