686 THE PALEONTOLOGY OF MINNESOTA. 



LCyllieiulliiV ruiiosa. 



CYTHERELLA ? RUGOSA Jones, and var. ARCTA, n. var. 



PLATE XLIII. FIGS. 21-25. 



Cytheropsis rugosa JONES, 1858. Ann. Mag. Nat. Hist, ser. 3, vol. i, p. 254, pi. x, flgs. 3 and 4; also 



1858. Geol. Sur. Can., dec-ade iii, p. 100. 

 Cytherellat rugosa JONKS, 1891. Contri. Can. Micro.-Pal., pt. iii, p. 99. 



SIZE. Length 0.9 mm.; night 0.58 mm.; thickness about 0.34 mm. Var. arcta, length 0.96 mm.: 

 bight 0.53 mm. Prof. Jones' type specimen is said to be 0.83 mm. long, and 0.54 mm. 

 high. 



Carapace small, blunt at the ends; outline subreniform, rounded at both ends, 

 the anterior one narrower than the other; of the upper and lower margins, one is 

 nearly straight; the other strongly convex. Surface coarsely pitted, the pitting 

 extending over all parts except a small spot situated, if we consider the straight 

 margin as dorsal, beneath the center of the valves. 



Fig. 25 represents a variety differing from the typical form in having the anterior 

 end drawn out. It may be called variety arcta. 



The generic position of this species is very doubtful . The typical form resembles 

 Aparchites minutissirnus, var. trentonensis, figured on the ssime plate, but the outline 

 of var. arcta is much more like that of Bythocypris cylindrica Hall (see plate XLIV). 

 It seems very doubtful to me that the species belongs to Cytherella, but as I am 

 unable to suggest a better arrangement, I have adopted Prof. Jones' latest suggestion. 



Formation and locality. Top of the Galena shales (Nematopora bed), near Cannon Falls, Minnesota. 

 Variety arcta is from the middle division of the Galena (Fusispira bed) near the same locality. 



Family CYPRIOTE. 

 Genus BYTHOCYPRIS, Brady. 



Bythocypris, BKADY, 1880. Kept. Ostracoda, "Challenger," p. 45; JOXES and KIKKHY, 1886, Ann. 

 Mag. Nat. Hist., ser. 5, vol. xviii, p. 250; also 1887, Proc. Geologist Assor., 

 veil, ix, p. 510; JONES, 1887, Ann. Mag. Nat. Hist., ser. 5, vol. xix, p. 184: 

 ULRICFI, 1890, Jour. Gin. Soc. Nat. Hist., vol. xiii, p. 196. 



Carapace smooth, more or less renifonb ; left valve larger than the right, over- 

 lapping it on both the dorsal and ventral margins; dorsal margin strongly convex, 

 ventral margin usually straight or slightly concave. 



This is a recent genus into which a number of Paleozic Ostracoda have been 

 placed by Prof. T. Rupert Jones and others. Whether this extension of the genus is 

 justified or not, I am unprepared to say. It seems to me, however, that some of the 

 species might with equal propriety be referred to other genera of the marine Cyprithr. 

 But as I have not given the subject the thought and time which its great difficulty 

 necessitates, my present judgment can have little value when opposed to that of 

 Prof. Jones. 



