Prof. T. R. Jones — On some Pakeozoic PhyUoj)oda. 351 



We are the more strengthened in otir opinion of the affinities of 

 these Palceozoic Crustacean shields, because their ornamentation 

 agrees with that of known Phyllopod carapaces, both in the minute 

 ridge-like, concentric lines of growth, and, in some cases, in the 

 delicate surface-ornament between them. 



It is to be observed also that these circular or ovate shields were 

 not originally flat discs or plates, but in many cases either sub- 

 conical or ridged, and herein unlike Aptychi, but resembling some 

 Phyllopods. Thus Discinocaris Browniana had a low conical surface : 

 Aspidocaris triasica was evidently conical, for the outer rim has 

 been radiately split owing to the flattening of the shield. SpatMo- 

 caris Emersonii and Lisgocaris Lutheri had elevated subconical cara- 

 paces. AptycJiopsis not unfrequently shows breakage resulting from 

 vertical compression ; and in Gardioc'aris we sometimes see a median 

 line or mark caused by a depression along the central portion. 

 Some forms, such as Dipterocaris procne, have the carapace bent 

 ridge-like along the middle of the back. The species now regarded 

 as characteristic and well defined are : — 



I. — Discinocaris. 



1. Discinocaris Broioniana, H. Woodward, 1866, Quart. Journ. 

 Geol. Soc. vol. xxii. p. 504, pi. 25, figs. 1, 5, 7. From the Anthi'acitic 

 Shales of the Moffat District, at Dobbs Linn, and Garpoolburn, 

 and in equivalent Silurian beds at Coalpit Ba,j, Co. Down, Ireland. 



2. D. dubia (Roemer), 1850. Referred to above. 



3. D. lata (H. Woodward), 1882. Geol. Mag. Dec. II. Vol. IX. 

 p. 388, PL IX. Fig. 13. 



This Mr. J. M. Clarke refers to Spathiocaris, but with us it is 

 accepted now as a Discinocaris, having concentric stri^, and an 

 angular notch. From the Upper Devonian of Biidesheim in the 

 Eifel, and Bicken in Nassau. 



4. D. triasica {Aspidocaris, Eeuss), 1867. Sitzungsb. k. Akad. 

 Wiss. Wien, vol. 55, pp. 1, etc., pi. (not numbered), figs. 1-5. 



Dr. A. E. von Reuss thought that this must be nearly allied to 

 Discinocaris, and so did Dr. Woodward, in the Geol. Mag. Dec. II. 

 Vol. IX. p. 368. It seems, indeed, to be really of that genus, though 

 a different species to any other we know. Von Reuss carefully 

 described and figured this species from the Raibl beds near Hallstadt. 



5. Discinocaris, sp. nov. 



In the Cambridge Museum is a broadly sagittate fossil shield, without 

 the cephalic portion, which appears to belong to a new species. From 

 the Coniston Mudstone (Up. Silurian), Skelgill Beck, near Ambleside. 



6. D. congener (Clarke), 1884. This is the Spathiocaris (Cardio- 

 caris^) congener, Clarke, N. Jahrb. f. Min., etc., 1884, i. p. 183, 

 pi. iv. fig. 5. It has the characters simply of Discinocaris. From 

 the Upper Devonian of Bicken, near Herborn, Nassau. 



7. D. ? gigas, H. Woodward, 1872. Geol. Mag. Vol. IX. p. 564. 

 Portions of a large carapace allied to Discinocaris, but somewhat 

 uncertain as to shape, have been found in the Moffat beds at Ettrick- 

 brigend, Selkirkshire, and in the Upper Silurian (Coniston Mud- 

 stone) of Skelgill Beck. 



