182 POST-TERTIARY ENTOMOSTRACA. 



what flattened arch, inferior distinctly sinuated in front of the middle and shghtly pro- 

 tuberant behind. Outline as seen from above elongato-ovate, widest behind the middle, 

 where the width is equal to little more than one third of the length, obtusely pointed in 

 front, posterior extremity rounded and shghtly indented in the middle. Hinge-pro- 

 cesses feebly developed (fig. 13), consisting of two shghtly elevated angular crests on the 

 right, and two slightly crenated sinuations on the left valve. Surface of the shell smooth, 

 ornamented with numerous, small, distantly scattered, circular papillae, and frequently 

 marked towards the extremities and along the ventral surface with more or less distinct 

 longitudinal furrows. 



Length, -^-th of an inch. 



This species, which is of frequent occurrence round the British shores at the present 

 day, seems to occupy, in some of its characters, especially in those of the hinge-joint, a 

 position intermediate between the genera Cythere and Ci/theridea. The animal structure 

 is, however, very distinct from that of the former genus, and, so far as we at present know, 

 does not differ from that observed in Cytheridea. 



Distribution. Recent. — Great Britain, Ireland, Bay of Biscay, Gulf of St. Law- 

 rence. 



Fossil. — England: Hopton Cliff. Scotland: Irvine. Ireland: New Docks at 

 Belfast, Portrush. 



Genus 4 — Eucytheue, Brady. 



Carapace high and compressed in front, lower and more tumid behind. Shell thin, 

 pellucid, and marked with conspicuous round white papillae. Hinge-joint formed on the 

 left valve by a projecting flange or crest, which is received into a corresponding depression 

 of the left valve. " Superior antennae five-jointed, and in structure almost like those of 

 Cythere; inferior much more robust, four-jointed; flagellum (urticating seta) long. 

 Mandibular palp three-jointed ; branchial appendage very small. Cutting portion of the 

 first maxillae weaker than usual ; internal segment rudimentary. Second pair of maxillae 

 very large, dilated in an extraordinary manner at the apex, flabelliform, and beset with 

 numerous apical setae. Feet weak and slender, subequal ; terminal claws long and almost 

 straight, alike in the male and female. Copulative organs of the male unusually small. 

 One eye." 



