660 THE PALEONTOLOGY OF MINNESOTA. 



[Euryi'hilhia recticulata. 



KTRYCHILINA RETICULATA Ulrich, and var. INCURVA, n. v<n: 



PLATE XLIV, FIGS. 1 and 2. 



Eurychilina reticulata ULKICH, 1889. Contri. to Can. Micro-Pal., pt. 2, p. 52, pi. ix, flgs. 9, 9a. 

 Not Eurychilina reticulata (Ulrich) JONES, 1890, Quart. Jour. Geol. Soc., vol. xlvi, p. 593, pi. xx, flgs. 



13a, 136. 



SIZE. Without marginal area, length 1.83 mm.: night 0.9 mm.; thickness 0.5 mm. 

 With " " " 2.40 " " 1.3 " 



Valves, excluding the marginal area, nearly semicircular in outline, straight 

 along the dorsal edge, moderately and almost uniformly convex; aulcus deep, extend- 

 ing half way across the body, not as wide as in the next species, its outline more 

 sharply defined behind and below than on the anterior side; above the sulcus expands 

 and becomes very shallow, while at the midlength it is constricted by a rounded 

 prominence on the posterior side; surface, except along the dorsal edge, beautifully 

 reticulate. Marginal area wide, narrowest posteriorly ; on the outer side it is flattened 

 or concave, and slopes inwardly, especially at the ends; ventrally the edge rises to 

 form a narrow, wavy, free border; surface marked by radial lines, strongest ventrally, 

 least distinct anteriorly; at its junction with the body of the valve, a more or less 

 elevated, linear ridge is usually present. Internal characters of valves and marginal 

 area almost exactly as in the next species (see plate XLIV, fig. 3.) 



This fine species is perhaps the most beautiful of all the Paleozoic Ostracoda 

 known to me, and when in a good state of preservation it is scarcely possible to 

 confound it with any other. Yet, as cited above, Prof. Jones has referred a Devonian 

 specimen from the Corniferous chert of New York to the same species. The 

 characters of the valve figured by him are preserved in an empty mold, which in 

 splitting the rock presented both an inner and an outer cast. Comparing these 

 with the Minnesota species, I am obliged to differ wtih Prof. Jones' determination. 

 Indeed, I doubt if they are even congeneric. The outline of the body of the valve 

 is not semicircular in the Devonian species but has that oblique form which is 

 commonly distinguished as "leperditoid." It is also proportionally a little higher, 

 the reticulate ornament extends to the dorsal edge, the sulcus is shorter and much 

 less defined, being merely a subcentral depression, and there is apparently no 

 rounded prominence behind it. Further, the dimensions given by Prof. Jones show 

 that his specimen is considerably larger than any Lower Silurian example of E. 

 retirulata so far seen, the length in the latter rarely, if ever, exceeding 2.5 mm., 

 while that of the Devonian form is stated to be 3.5 mm. These differences, if no 

 others existed, would be sufficient to prove a distinct species. 



Hut they are not all, since his fig. 136 shows that the border was convex exteriorly 

 while it should be Hat or concave; and in fig. 13, representing an impression of the 



