674 THE PALEONTOLOGY OF MINNESOTA. 



[Qtenobolbina fulorata. 



This genus includes a well marked group of paleozoic Ostracoda, distinguished, 

 in its typical development, from all the other genera of the family by the bulbous 

 character of the posterior end. A small isolated middle lobe, which is the most 

 persistent character of Beyrichia and Klosdenia, is, except in one case, never present, 

 the central lobe or ridge, when one has been divided off from the anterior swelling 

 of the surface, being united ventrally with the large posterior lobe. A small lobe 

 is isolated in C. tumida Ulrich, but as the posterior half is decidedly bulbous in this 

 species it may be advisable to leave it with this genus. Still, I have fully satisfied 

 myself that it is a close ally, perhaps a progenitor of the (^linton Beyrichia lata Van- 

 uxem, and that is not far from B. kloedini McCoy. 



Ctenoholbina has its best development in the Cincinnati group, from which four 

 or five good species and two varieties have been described. Two Trenton species, 

 differing from the Cincinnati types in the lesser development of the posterior bulb, 

 are found in Minnesota. C. punctata Ulrich, of the Niagara, retains the generic 

 characters very well, as does also , C. papillosa Ulrich, of the Devonian, while C. 

 informis Ulrich, also Devonian, reminds of the Trenton C. crassa. C. minima, of the 

 Hamilton, is much like C. hispinosa from Cincinnati, and both are almost primitian 

 in their simplicity. Of European species I know of only one that has the characters 

 of Ctenoholbina clearly developed. This is the Beyrichia gitillieri Fromelin, as figured 

 by Jones, in 1890, (Quart. Jour. Geol. Soc, vol 46, pi. 21, figs. 2a, b, c). It is closely 

 related to G. ciliata and occurs in the Lower Silurian strata of France. Another, 

 that is as much of a Ctenob'olbina as C. crassa, C.fulcrata and C. informis, is the Bollia? 

 (luricularis Jones and Holl, from the Wenlock of England. Indeed, these four 

 species are closely related and cannot justly be separated generically, -so that I 

 propose to refer the Wenlock species als6 to this genus. Prof. Jones concedes in a 

 letter to me that the auricularis is not a Bollia, and a close comparison with the 

 Minnesota species mentioned proves to me that my former opinion of the British 

 species, when I thought that it might belong to Halliella (Jour. Cin. Soc. Nat. Hist., 

 vol. 13, p, 185), is erroneous. 



Ctenobolbina fulorata, n. sp. 



PLATE XLIV, FIGS. 8-11. 



Size.— Length 1.2 mm.; bight 0.78 mm.; thickness 0.56 mm. 

 Length 1.2 mm.; hight 0.80 mm.; thickness 0.60 mm. 



Valves obliquely subovate, highest posteriorly, with the back straight and the 

 dorsal angles usually well defined. Posterior bulb comparatively narrow; sulcus deep, 

 wide, oblique, curving backward below; anterior lobe undivided, larger than the 

 posterior, in some specimens less oblique than in others; ventral and posterior sides 



