SILURIAN- OSTRA.CODA FROM NORTH AMERICA, ETC. 543 



P. punctulifera in a thin limestone composed of the usual frag- 

 ments and small organisms, and are — ■ 



(1) Primitia Walcotti, sp. no v. ; and (2) Ulriehia Com^adi, gen. 

 et sp. nov. 



12. Primitia (?) Walcotti, sp. nov. 



Length -95 mm. ; height -47 mm. 



An oblong Primitia'^ (woodcut, fig. 1), imperfect at one end, 

 with a central pit, and elegantly ornamented with narrow curved 

 ridges and furrows (of about equal width). These are nearly 

 straight, and somewhat inosculating on the dorsal, tortuous and 



Fig. 1. — Primitia Walcotti, sp, nov. (Magn. 40 diam.) 

 From Thedford, Canada. Coll. Dr. Hinde. F.G.S. 



interrupted on the ventral region. Small pits occur here and there 

 along the furrows, as if marking obsolete meshes. 



This I name P. Walcotti, in honour of C. D. Walcott, P.G.S., of 

 Washington, U.S., who has discovered and described several very 

 interesting forms of IN^orth-American Ostracoda. 



YIII. Genus Ulrichia, nov. 



Among the Primitice which have the normal medio-dorsal sulcus, 

 there are many having the edges of the sulcus more or less swollen, 

 sometimes on one, and sometimes on both sides. The varieties of 

 Primitia mundula often show this modification in some degree. 

 This varietal feature, however, becomes so much exaggerated as to 

 obliterate the sulcus by the presence of two large tubercles, mostly 

 without a definite pit or furrow between them. This is seen in 

 P. bicornis, J., ' Ann. & Mag. Nat. Hist.' ser. 2, vol. xvi. (1855), 

 p. 173, pi. vi. fig. 23, and op. cit. ser. 3, vol. xvi. (1865), p. 420 ; in 

 P. cequalis^, J. &H., op. cit. ser. 5, vol. xvii. (1886), p. 412, pi. xiv. 

 fig. 11 ; in P. Morgani, J., Q. J. G. S. February 1890, p. 5, pi. iv. 

 fig. 6 ; and in a species now described, and dedicated to T. A. 

 Conrad. Mr. E. 0. Ulrich, of the Illinois Geological Survey, has 

 shown me sketches of somewhat similar forms from the Lower 

 Silurian at Corryville and Fairmount, near Cincinnati. As all 



* P. diversa and P. cornuta, J. & H. (op. cit. figs. 10 & 12), are also regarded 

 as having tubercles which, although far apart, represent "essentially the 

 eleyated sides of the modified dorsal furrow " (op. cit. p. 412). 



