56 Prof. T. R. Jones and Dr. H. B. Holl on 
As one valve does not overlap the other in this Entomos- 
tracan, it is not a Leperditia; and the absence of both eye- 
spot and muscle-spot also distinguishes it from that form and 
the allied Jsochilina. The acutely elliptical depression of 
the dorsal margins and the ventral rims remind us of similar 
features in Primitia cristata, P. umbilicata, and P. tersa (Ann. 
Nat. Hist. /.c. pl. 13. figs. 1-3) ; and a ventral rim is charac- 
teristic also of other Primitiw, whether the median pit or fur- 
row 1s present or not. 
P. Maccoyii is very abundant in the limestone of the Chair 
of Kildare. 
Several years since, Mr. Salter intimated that this fossil 
could not be the same as Hisinger’s Cythere phaseolus. ‘The 
latter, we know, is a Leperditia closely related to (or the young 
of) L. Balthica; and, though figured roughly in Hisinger’s 
‘ Lethzea Suecica’ (pl. 1. fig. 1), with a mere ovate outline (as, 
indeed, L. Balthica also was at first), it is really Leperditioid 
in shape, and has other characters of the genus. 
An individual P. Maccoyii is present in one of the specimens 
of Bala-Caradoc limestone from Aldeans*, on the Stincher 
(or Stinchar) River,in Ayrshire, preserved in the W oodwardian 
Museum at Cambridge, and, indeed, appears to have been no- 
ticed, though not recognized, by Prof. M‘Coy (see Ann. Nat. 
Hist. ser. 2. vol. viii. p. 387; and further on, p. 60). 
In the equivalent limestone of Keisley, in Westmoreland, 
which has a close affinity, both in fossils and mineral charac- 
ter, with that of the Chair of Kildare, P. Maccoy7i has been 
discovered by Prof. Harkness (see his account of the Lower 
Silurian Rocks of Westmoreland, Quart. Journ. Geol. Soc. 
vol. xxi. pp. 243 &c.). 
2. Primitia Sancti-Patrict’, n. sp. Pl. VII. figs. 4a, 46. 
Carapace smooth, almost semicircular in outline, convex in 
the middle and nearly equally compressed towards the margin 
all round; back very slightly arched, rounded at the end of 
the hinge-line ; one extremity rather more broadly curved than 
the other; ventral margin fully convex, and bordered (espe- 
cially posteriorly) with a faint rim where the edge of the valve 
turns inward. Dorsal profile acute-oval. 
Rather more semicircular than P. obsoleta, this Irish species 
differs from it also in having less of the marginal rim and no 
sulcus, and in being more oval than ovate in the profile of the 
closed valves. Indeed it seems to be intermediate between P. 
* Also written Aldens and Aldons. 
t Rep. Brit. Assoc. for 1850, Trans. Sect. p. 107; Quart. Journ. Geol. 
Soe. vol. viii, (1851) pp. 189 &c. ; and ‘Siluria,’ 3rd edit. 1867, p. 156, 
