Report on Palceozoic Phyllopoda. 29 



Dithyrocnris 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 

 Clark 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 ; mure or less 

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

 on the front and hind borders. The antero-doi'sal region ends with 

 a blunt angle or a short process ; and the postero-ventral wil;h 

 a strong, sharp, trigonal spine. 



The straight hinge-line is defined by two small dorsal notches. 

 The ventral border has a striated, serrated, or fringed margin, either 

 on its posterior moiety or throughout its extent. 



The surface of each valve bears one longitudinal (meso-lateral) 

 ridge, and sometimes others parallel ; also short ridges {cephalic) 

 over the gastric apparatus, and slighter ridges (nuchal) near the top 

 of the dorsal ridge, all more or less rugose. 



Scattered granulations and tubercles are often pi'esent on some 

 parts of the valves, also lines and reticulations. 



Granulation is feeble and sparse on D. glabra and D. ovalis ; 

 strong and abundant on D. granulata. Small prickles, rising from 

 the meshes of a reticulation, are scattered over D. tricornis, D. Colei, 

 and D. orbicularis (?). A system of oblique transverse lines 

 characterizes D. testudinea. A feeble reticulation is traceable ou 

 D. funiculata and D. Scouleri (?). Longitudinal strise mark the 

 surface in D. Belli and D. striata ; and D. tennistriata and 

 D. Youngii have longitudinal costulae. 



In consideration of certain diiferences in the carapaces, wo 

 separate Nos. 10 and 11 of the Table, at p. 28, from Dithyrocaris, 

 as Chmiocaris tenuistriata and Cli. Youngii, the carapace being 

 bivalved and gaping. There is also an obscure Devonian form, 

 from Saalfeld, to which we refer as CJicenocaris Bichteriana. 

 We regard No. 12 as having a closed bivalved test, and therefore 

 designate it as Calyptocaris striata. 



We have had the opportunity of studying an old Apus-like 

 fossil ^ labelled ' Burdiehouse.' It shows a small circular carapace 

 (measuring 15 by 13 mm.), with strong postero-ventral angles, and 

 distinct meso-lateral ridges leading to them ; also a slightly curved 

 depression in the middle of the front border, and a granulated 

 margin throughout. 



Mr. E. J. Garwood, F.G.S., who is a member of the British 

 Association Committee for defining the zones in the Carboniferous 



^ Sibbertia orbicularis. 



