500 TEANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



is the slight calcification of the fused terga and pleura. 

 The only portion of the dorsal shield which is at all 

 heavily calcified is the "cephalic" region bounded 

 behind and at the sides by very deep grooves (Text-fig 1). 

 The branchiostegite is almost membranous and the 

 cardiac portion of the carapace is only lightly calcified in 

 its anterior portion. On the anterior border there is a 

 median pointed triangular rostrum of small size, and on 

 either side of it, separated by long shallow excavations, 

 are two supra-orbital prominences.* The front now 

 becomes continuous laterally with deep grooves, which 

 pass back to join the cervical groove. The branchio- 

 stegite is hinged to the groove on both sides. It drops 

 vertically downwards anteriorly, almost at right angles 

 to the dorsal shield, but the angle becomes gradually less 

 acute further back, till in the thoracic region the lateral 

 walls form a smooth curve with the dorsal side. Were 

 the body not so narrow, the appendages would present an 

 obstacle to the animal retiring into its shell. As it is, 

 they can be folded up beside the body in a very small 

 space. The proximal joints are flattened considerably 

 from side to side to reduce the size of the animal when 

 it is in its shell. 



The lateral border of the cephalothorax is prolonged 

 forwards to form a considerable lobe on either side, which 

 projects on a level with the end of the rostrum. This 

 lobe is supported dorsally by its folded and calcified edge. 



The hind border of the carapace is reflexed and 

 attached to the eighth thoracic somite, the tergum of 

 which is partially separate. Certain lines and areas are 

 recognisable on the carapace. The most important of 

 these is the groove corresponding to the cervical groove 



* The front between the supra-orbital lobes in E. prideauxii 

 is almost linear. 



