520 



REPORT — 1898. 



Dithyrocaris has a clypeiform test ; at all events most of the specimens 

 have a shield-like test, readily dividing into two moieties or valves ; but 

 some specimens seem to support the idea of having been able to fold the 

 two sides together. The moieties are often separate, and some are too 

 convex to have formed a quite flat shield ; some have the lateral edges 

 turned sharply downwards and inwards. 



The valves, or two lateral moieties, were united along their dorsal 

 edges simply ; several specimens, however, had a dorsal rugose ridge-plate, 

 over-riding, narrow, and longitudinal (somewhat like that described as an 

 intervening plate in Mesothyra by Hall and Clarke in 1888), ending in a 

 posterior spine. 



The valves are sub-oblong, straight along the middle two-thirds of the 

 dorsal border, and elliptically curved ventrally ; more or less rounded at 

 the ends, with a median hollow or notch at their junction on the front 

 and hind borders. The antero-dorsal region ends with a blunt angle or a 



