Jones and Sherhorn — Tertiary Entomostraca. 453 



circular than the hinder. Surface coarsely reticulate ; the reticulations 

 becoming more .shallow and indistinct as they reach the central area. 

 Many of the ridges of the meshes are pinched up at their junctions, 

 and in most cases thus form bluntly-pointed spines ; these spinous 

 prolongations are partly the cause of the confusion of the reticula- 

 tion in the central area. Approaching the margins, the 

 SjDines become longer and more defined ; and the 

 anterior area bears, in addition to its marginal row of 

 spines, a second row just within the other. In this 

 form, related to C. Bowerbanlciana, on the one hand, 

 and to C. liorrescens on the other, we note that the 

 characteristic ventral ridge of spines, which is pre 

 sent in both these forms, is absent, being merely re- 

 presented by scattered spines, not arranged in a 

 definite order except on the anterior area. The Fig. 2. — Cythe- 



reticulation is also much more distinct, — a marked '"':'* spmossis- 

 r . . ., r. sima, sp. nov. 



leature m the new lorm. 



To this same group belongs a rather common recent and Post- 

 Tertiary species, namely, Cythereis Dunelmensis, Norman (the refer- 

 ences are given in full in the " Monogr. Post-Tert, Entom." 1874, 

 p. 168). The chief differences between this and the older form from 

 the London Clay are in the shape of the posterior margin, which is 

 elliptically rounded in the latter instead of being square, and a more 

 definitely spinose, instead of foliaceous, condition of the ornament, 

 especially towards the margins. 



Two valves only : from Piccadilly. Sherborn and Chapman Col- 

 lection. 



40. Cythereis akanea, sp. nov. PI. XL Fig. 10a, 106. 



Oblong, with the front margin broader and rounder than the 

 hinder, both more or less denticulate. The surface ornamented with 

 a delicate raised network of irregular meshes, which extend over the 

 flat ventral area. Two ridges, over which the network is traceable, 

 are present. One, shorter than the other, occupies the median line 

 fi'om about the centre to the edge of the posterior slope, which makes 

 a strong depression at the hind margin. The other and longer ridge 

 commences in a curve inside the front margin, rises as it borders the 

 ventral region, and dies out at the posterior slope, like the other. 

 The ventral aspect of the carapace is cuneiform or almost sagittate. 

 C. SaidingPA-i, Bosquet, ' Tert. Entom.,' p. 125, pi. vi. fig. 10, is 

 near to this species in general characters ; but its more angular 

 shape, and more symmetrical network distinguish it. So also C. 

 Edioardsii (Eoemer), Eeuss, 'Haidinger's Nat. Abth.' vol. iii. p. 84, 

 pi. X. fig. 24, is like it to some extent ; but its ridges extend the 

 whole length of the valve, joining fore and aft, and, as figured by 

 Bosquet, ' Entom. Tert.' p. 94, pi. iv. fig. 14, it appears still coarser 

 or stronger, and with still more marked features. 



Several specimens from the London Clay ; Piccadilly, London. 

 Sherborn and Chapman Collection. 



