1 PROP. T. E. JONES ON SOME PALAEOZOIC OSTKACODA 



front than behind, the anterior third sloping gentlj-, and the 

 posterior more suddenly to the margin (figs. 12 6 and 13 b) ; a 

 reticulate surface-ornament supplies the " minute puncta or pits " 

 of the original description, but dies out at each end (in the Scandi- 

 navian Primitiopsis only in front), and there are three small, smooth 

 tubercles, oue central and two on the posterior region ; the meshes 

 are more distinct just round the middle tubercle. Eig. 7 is more 

 oblong and flatter, but the features may have been produced by 

 pressure, as the outline of the united valves (fig. 7 h) is not sym- 

 metrical, and the postero-dorsal edge has been damaged ; the reti- 

 culation, not so strongly pronounced, reaches to the end-margins, 

 though weak just there; the central tubercle is represented by a 

 spot of stronger meshes a little in advance of the centre, and the 

 two posteiior tubercles are present. 



The original specimens were from the Hamilton Group (often 

 abundant on the shaly laminae), from the shores of Lake Eiie to 

 Canandaigua Lake, N.Y. The specimens hero figured are : fig. 7 

 from the Hamilton Group, at Seneca Lake, JST.Y. ; fig. 12, in a dark 

 argillaceous schistose rock, with calcareous organisms, from Darien, 

 N.Y. ; fig. 13, also from the Hamilton Group, at Eighteen-mile 

 Creek, Lake Erie. 



III. Genus Entomis, Jones. 



Entomis, Jones, ' Ann. & Mag. Nat. Hist.' ser. 4, vol. xi. 1873, 

 p. 413. 



1. Entomis ehomboidea, sp. nov. (PI. II. figs. 9, 10 a, h.) 



Length. Breadth. Thickness, 

 njra. mm. mm. 



^^^'^ I 10 1-0 -46 -48 



Both of these specimens have probably suffered from pressure ; 

 but fig. 10, having the sulcus in its normal vertical position, has 

 apparently best preserved the original shape, lihomboidal, straight 

 above and below, with the ends obliquely rounded, unequally in 

 fig. 10 «.. Surface flattish and sloping rapidly down at the free 

 margins, especially posteriorly (fig. 10 6); impressed with a definite 

 dorsal sulcus ; ornamented with numerous strong, longitudinal, 

 but inosculating raised striaG, or thin wrinkles, with a tendency to 

 become concentric, as more fully expressed in K concentrica (Do 

 Koninck) and JE. hicoticentr'ica, Jones. 



In fig. 9 the valve is more truly rhomboidal, with the sulcus 

 oblique (probably by pressure), and parallel to the truncated sloping 

 ends, which are equal, and have their angles rounded, with one pair 

 of the alternate angles less rounded than the other. 



Oblong and subrhomboidal forms of Entomis are indicated by 

 figs. 19, 20, 21, pi. iv. ' Monogr. Carbonif, Cypridinada?, Pal. Soc.' 

 1874 ; and by fig. 7 (oblique by pressure), pi. xi. ' A. M. N. H.' 

 September 1879. 



