340 On some Palmozoic Ostracoda. — Jones. 
however, that they were not originally so, but that the oxide of iron 
has replaced the original carbonate of lime. In short, my impression 
is that the rock was once a calcareous oolite, but in the course of time 
has been altered by pressure and chemical changes. In this way the 
original structure of the granules has been modified, and their 
nuclei have disappeared. When tested with hydrochloric acid, con- 
siderable effervescence takes place, due to the presence of carbonate 
of lime ; but the rock as a limestone is impure. 
II. Silurian Species. Figs. 3-9. 
I. BYTHOCYPRis oviFORMis. Sp. nov. Figs. 3a-3c. 
Carapace, very small, about .66 mm. long, almost egg-shaped, 
but unequally convex on the upper and lower margins, and 
too much narrowed and compressed anteriorly to be truly 
ovate. The left valve is by far the larger, as in Bythocypris; 
and the dorsal edge of the left valve is much thickened in the 
middle, where it strongly overlaps the other valve. The sur- 
face is minutely punctate. Another, rather smaller, specimen 
(imperfect) occurs with the same superficial ornament. 
From the dark-colored Lewistown shaly limestone of the- 
Lower Heldeberg group, Perry county Pa., and probably 
equivalent to the "Ludlow" beds of England. 
2. LEPERDITIA SUBQUADRATA. Sp. nOV. Figs. 'Ja-4d. 
This very small carapace, subquadrate in outline, and mod- 
erately convex, shows the ventral overlap distinctive of 
Leperdltia. In outline and contour it somewhat resembles 
L. nana Jones, ("Ann. Mag. N. H." ser. 3, vol. i (1858), p. 
244, pi. 9, fig. 12 ; L. canadensis^ var. nana^ op. cit. 1881, p. 
343) ; but its ends are more semicircular. In Dr. James 
Hall's Lep. (Isochilina) minutissma, "24th Report State 
Cabinet, N. Y." 1872, p. 231, pi. 8, fig. 13, and "Geol. Survey 
Ohio," vol. 11, part 2 (1875), p. 102, pi. 4. fig. 4, the ends are 
unequal ; his L. hudsonica is like it in outline, but is larger 
and much more convex. Another little Leperditia (Z. ovata 
Jones "Ann. Mag. N. H." ser. 3, vol. i, 1858,^ p. 252, pi. 10. fig. 
14) is known from Pennsylvania. It is from a lower horizon 
and is more ovate and convex. The shape of the Carbonifer- 
ous L. scotolurdigalensis (probably a dwarf form of L. okeni) 
also approaches that of the specimen under notice, but it is 
* Alluding to this paper and plate, I may mention that figs. 15, 16, 
17 and 18 are all Beyrichia pejinsijlvanica ; but figs. 16, 17 and 18 are 
destitute of the marginal fringe, which, present in fig. 15, led to the 
mistake of the figure being referred to B. vKuxoyiana. 8ee also "Ann. 
M. N. H." ser. 5, vol. xvii (1886). p. 347, note. 
