674 THE PALEON'TOLOGY OF MINNESOTA. 
[Ctenobolbina fulcrata. 
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 Kladenia, 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 Clinton Beyrichia lata Van- 
uxem, and that is not far from B. kladini McCoy. 
Ctenobolbina 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. 
infurmis Ulrich, also Devonian, reminds of the Trenton C. crassa. C. minima, of the 
Hamilton, is much like C. bispinosa from Cincinnati, and both are almost primitian 
in their simplicity. Of European species I know of only one that has the characters 
of Ctenobolbina clearly developed. This is the Beyrichia guilliert Fromelin, as figured 
by Jones, in 1890, (Quart. Jour. Geol. Soc., vol 46, pl. 21, figs. 2a, 6, c). It is closely 
related to C. ciliata and occurs in the Lower Silurian strata of France. Another, 
that isas much ofa Clenobolbina as C. crassa, C. fulcrata and C. informis, is the Bollia ? 
auricularis Jones and Holl, from the Wenlock of HEngland. Indeed, these four 
species are closely related and cannot justly be separated generically, so that I 
propose to refer the Wenlock species also to this genus. Prof. Jones concedes in a 
letter to me that the awricularis 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 FULCRATA, 7”. Sp. 
PLATE XLIV, FIGS. 8—11. 
Sizze.—Length 1.2 mm.; hight 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 x: 
