462 Synopsis of the Genera of Fossil Phyllopoda. 
b- 
| ai | $33 
Geological GENERA. Special character. a8 cee 
Stage. os gee 
Se | Bes 
ze | 2 
Sn A I ol RE 
I. Carapace UNIVALVE. 
(I.) Fuar SHrevp. 
1. Neither sutured nor ridged along the back. 
(A). Posterior border entire. (Far behind.) 
Silurian ..... ( Discinocaris, H. W., 1866. ..... Angular notch* .......... Ave Hee ae, 
De 
Raibl beds 
(Trias, 
Hallstadt) | Aspidocaris, Reuss., 1867.......... Angular notch* 
* Round shield. 
Devonian... Spathocaris, Clarke, 1882.......... Angular notch. tT 
Devonian... Phoelodocaris, H. W., 1882. ..... Sinuous notch.t 
Devonian..... Iisgocaris, Clarke, 1882. .......... Oblong -notch. fF 
Devonian... Ellipsocaris, H. W., 1882.......... Rounded notch.t 
-+These shields 
differ in shape. 
(B.) Posterior border slightly notched. 
Devonian..... Cardiocaris, H. W., 1882.......... | Front notch oblong. | 
(C.) Posterior border deeply notched. (Open behind.) 
Silurian ..... ? Pterocaris, Barrande, 1882..... Both notches angular 
(test radiately 
Lower Silu- marked). 
rian and 
Devonian Dipterocaris, Clarke, 1883. ..... Both notches angular. 
2. Ridged along the back. (Like Apus.) 
Carbonif. & ( Dithyrocaris, Scouler, 1848 ..... Ridged and  some- 
Devonian | (Argas, Scouler, 1835) ..... times prickled. 1, 4, 
ai or 6 3 
Carbon- | 
iferous ..... | Rachwra, Scudder, 1878 ........ (Telson only known.)| — | 38 
3. Sutured along the back. 
Silurian .... A. Aptychopsis, Barrande (and | Angular notch. 
EL Wis) 5 EBT 2 oe case utes | 
Lower Silu- 
TAM os. oe: B. Peltocaris, Salter, 1863... Rounded notch... 4? 4? 
Lower Silu- 
WIAA 22, C. Pinnocaris,R. E., jun., 1878 | Slight notch: _ strie 
concentric far back. 
Silurian... D.? Crescentilla, Barr., 1872 | Notched before and 
behind. 
