422 Prof. T. ft. Jones and Dr. H. B. Holl on 



strongly overlapped on its ventral border. A slight impression 

 on the middle of the valves, and the nearly equivalved condition, 

 characterize this as a Frimitia, in spite of its Leperditia-Yike 

 outline, — the last being a feature taken on by other Primitice, as 

 we have already shown. The most convex portion of the surface 

 is faintly and irregularly corrugated by broadish shallow pits, 

 which enlarge towards the middle, and there merge into the 

 feeble sulcus. From the Wenlock Limestone of Crofts Quarry, 

 near West Malvern. 



19. Primitia Beyrichiana, nov. PI. XIII. fig. 9. 



Length ~, height T V inch (as 3 to 2). 



Carapace-valve suboblong, straight along the back, boldly 

 curved behind, gently convex ventrally, obliquely truncate with 

 a gentle curve in front. Surface convex, and marked with a 

 broad, subtriangular, faint impression in the middle of the dorsal 

 region ; and, excepting on the dorsal edge, margined with a neat 

 flattened rim, rather narrower at the anterior edge than elsewhere, 

 and uniformly sculptured with minute elongate pits, perpendi- 

 cular to the peripheral curve of the valve, and thus forming a 

 radiate ornament. Such a style of margin is present also in P. 

 Roemeriana, and is still more developed in Beyrichia Maccoyiana ; 

 and a simply pitted rim is found in B. Salteriana, Isochilina 

 gracilis, &c. 



P. Beyrichiana is rare, and is one of the small Bivalve Entomo- 

 straca referred to (under the terms Ci/theres, and Cytheropses) in 

 Ann. Nat. Hist. ser. 2. vol. xvi. p. 84, and ser. 3. vol. i. p. 249, 

 as abounding in the drifted Scandinavian blocks of Upper 

 Silurian Limestone found in North Germany, with some of which 

 material Prof. E. Beyrich, the eminent palaeontologist at Berlin, 

 long ago supplied us. 



20. Primitia Roemeriana, nov. PI. XIII. figs. 8 a, b. 



Length —;Hro> height t |g , thickness -, ■% g inch. 



Carapace ovate, back-line less convex than the ventral border. 

 Valves convex, bearing a very faint subcentral impression, and 

 marked with numerous, small, roundish, shallow pits, the inter- 

 vening surface being a smooth, nearly regular meshwork (like 

 the pattern on the side of a thimble). The valves are also bor- 

 dered with a fiat marginal rim, broadest ventrally, thinning away 

 at the dorsal slopes, and neatly ornamented with a row of minute 

 subquadrate pits, forming a radiate fringe, as in P. Beyrichiana. 

 The ventral profile of the united valves is acutely ovate. 



This ornamented species, differing markedly from the pretty 

 radiated P. Beyrichiana of Sweden, is from the Wenlock Limestone 

 of the Crofts near Malvern ; and we name it after our friend 



