Professor Emerson on HalVs Geological Collections. 581 



gothlands Cambriska ocli Siluriska Aliagringar, p. 85, fig. 70), from the Triuu- 

 clid Skifier of Swetleu accouipauy the typical forms. 

 PrIMITIA FROBISHEKI, II. s. 



Carapace-valve smooth, light-brown, nearly oval, sti'ongly and regularly 

 convex, sloping away from the central portion to meet the 

 road reflected border at right angles. This border is broad- 

 est on the ventral side ; is thin and must have been ap- 

 j)lied to the corresponding margin of the left valve like 

 a flange. On this margin are place<l 9-10 distinct ex- Fig. g „ c^gt of right 

 tremely thin elevated ribs, which run up onto the valve valvp, x 4 ; fig. 8 h, 



.,.,-, . T T, n .-, -1 11 T more cTilarged to show 



towards a central point ni the middle of the dorsal border; ^.j^^^ Length u mm.- 

 of these ribs only six are preserved. From the ventral breadth, | mm. 

 furrow they may be traced up the valve so for as the shell is present, retaining 

 their radial direction, and not anastomosing as is the case in more recent genera. 

 Just in advance of the middle line of the valve a furrow commences, shallow at the 

 dorsal border, grows narrower and much deeper, and ends abruptly at the middle 

 of the valve, being reijresented in the interior by a strong elevation which rises 

 nearly to the center of the carapace. This furrow borders at its deepest portion 

 a proportionally large hemispherical elevated tubercle, which passes into the gen- 

 eral convexity of the valve without the intervention of any depression except upon 

 the posterior side and for a short distance round onto the under side, where it is 

 bounded by a shallow furrow prolonged from the central sulcus. The description is 

 drawn up from a cast of the interior of a right valve having the shell remaining upon 

 the border and half-way up the side and from the interiors of several valves in 

 good ijreservation. It is allied to the Byrichia strangidata, Jones, An. l^nt. Hist. 

 1855, 2d series, xvi, p. 172, = Primitia nana, Jones and Hall, loc. cit, 3d series, 

 xvi, 1865, p. 420, from English Lower Silurian ; also to P. strangulata, Jones, in 

 Linnarsson Vestergoth. Camb. o. Sil. Af., p. 85. Difters in the broad-ribbed mar- 

 gin, large size, lower position of tubercle and greater convexity. A form which 

 I have not found described occurs in the Tentaculite limestone of Schoharie with 

 L. alta, which agrees closely with the above-described species. The state of 

 preservation made it not possible to determine if the marginal ribs were present. 



Found in the gray limestone with other Entomostraca. 

 Byrichia symmetrica, n. s. 



Carapace- valve flattened, elongate. Dorsal and ventral margins parallel. 

 Extremities rounded about equally, meeting the dorsal border with slight and 

 equal angles. Dorsal marging straight, not quite equaling the longest diameter 

 of the valve. Valve ornamented l)y two irreguhuly -rounded tubercles, the ante- 



