Paleozoic Bivalved Entomostraca. 253 



posed oi Beyrichia {B. Pennsylvanica) , from the limestone-bands 

 of the marls of the Scalent series of Pennsylvania. 



6. Beyrichia Pennsylvanica, spec. nov. PI. X. figs. 16-18. 



Length ^V, breadth ^'^ inch. 



Carapace- valves small, varying from oblong to nearly reniform, 

 convex, coarsely punctate or reticulate, and marked by two short 

 dorsal notches, which are variable in their development. Some- 

 times the anterior notch is obsolete (see fig. 16), — probably a 

 condition of the young state, — giving the valve a unisulcate 

 appearance. Sometimes the two notches encircle a small roundish 

 lobe (fig. 17) ; but usually they are distinct, and separated by the 

 central lobe of the valve^s surface (fig. 18). Many conditions 

 intermediate to these occur. 



In its one-notched state, this species much resembles B. stran- 

 gulata, and in its fully-developed trilobed form it resembles 

 some varieties of B. Kloedeni, on the one hand, and B. clathrata 

 of Beechey Island, on the other : but it is certainly distinct from 

 either. 



Innumerable individuals of this Beyrichia, of different stages 

 of growth, are present in the limestone-bands in the marls of the 

 Scalent group of Pennsylvania (Onondaga Salt group). Some 

 of this hard calcareous rock, which is dark-grey internally, but 

 weathers of a lighter and ferruginous grey, is almost composed of 

 the Beyrichia, and is traversed by very fine parallel linear fissures, 

 occupied by calc-spar. 



The same species occurs in equal numbers, in company with 

 B. Maccoyianttj in a somewhat similar rock of the same forma- 

 tion, but softer, more flaky, and not traversed by cleavage- 

 lines, 



I have found two individuals of apparently a smooth variety 

 of this species, showing the three lobes, as in fig. 18, in the 

 greyish limestone from near Barre Forge, where it is associated 

 with Leper ditia Pennsylvanica. 



7. Leper ditia [Isochilina) cylindrica (?), Hall, Palaeontology of 

 New York, vol. ii. p. 14. pi. 4. fig. 8. 



Under the name of " Gytherina cylindrica," Prof. James Hall 

 has noticed and figured some Entomostraca in the " Medina 

 Sandstone'^ of Orleans County ; and though these figures and 

 description are of little service in the identification of the species, 

 yet, having examined some apparently similar specimens also in 

 Medina sandstone, 1 offer some remarks on the subject, espe- 



