OSTKACODA. 345 



upon the head, and they are exceptionally large in point of 

 size. Aristozoe reaches sometimes the extraordinary length 

 of three inches. Primitia (fig. 201, E-G) is another ancient 

 type, essentially Silurian in its distribution, and characterised 

 by its equivalve, convex, oblong carapace, indented with a 

 vertical dorsal groove of variable depth. Eelated to Primitia 

 is the genus Beyrichia (fig. 201, H and i), which ranges from 

 the Silurian to the Carboniferous, and is more particularly 

 distinguished by the possession of two or three transverse 

 grooves, which start at the hinge, and pass partially or 

 wholly across the valves. In the curious Beyrichia oculi- 

 fera, the eye-spot forms a prominent and faceted tubercle, 

 unlike that of any other Ostracode (fig. 201, i). Two other 

 members of the ancient family of the Leperditiadce may be 

 just mentioned namely, Kirkbya and Moorea, both com- 

 mencing in the Upper Silurian, and ranging, the former to 

 the Permian, and the latter to the Carboniferous. 



Another great group of Ostracoda is that of the Cypri- 

 dinadce, with numerous living forms, and represented in past 

 time principally by 'the three generic types, Cypridina, 

 Entomis, and Entomoconchus, the last two of these being 

 entirely extinct. In Cypridina (fig. 201, L) the carapace is 

 produced in front into a beak-like projection, below which 

 is a hollow or notch facing the ventral margin. Many of 

 the so-called Cypridince of the older Palseozoic rocks are 

 now known to be referable to other types, but the genus 

 is well represented in the Carboniferous, and exists at the 

 present day. Entoinis (fig. 201, J and K) is a Silurian and 

 Devonian genus, which resembles some of the Leperditiadce 

 in having a dorsal groove, indenting the valves transversely, 

 and sometimes reaching the ventral margin, and having a 

 rounded tubercle placed below its lower end. One species 

 of this genus, formerly known as a Cypridina, is so abundant 

 in certain of the Devonian strata of Germany as to have 

 gained for these the name of " Cypridinen-Schiefer. " Ento- 

 moconchus (fig. 201, M), again, is a large form, with a thick 

 and globose carapace, having a much less developed notch 

 in front than in Cypridina. It is confined to the Carbon- 

 iferous rocks. Among other Carboniferous Cypridinadce may 



