364 ON A NEW SPECIES OF AGELACRINITES, 
not yet established. For these reasons 1 weuld suggest the term 
THyRoIpDA, i allusion to the valved aperture, as the name of the 
special group or order framed for the reception of these forms. The 
following scheme will then represent the probable relations of the 
various leading groups belonging to the Echinodermata generally : 
Crinoida. 
Biastoida. 
Cystidea.——, 
Thyroida——, 
| Asterida. 
Ophiurida. 
| Ruryalida. 
Eeninida. 
Holothurida. 
In the group Tuyrorpa, we have, at present, but one Family— 
that of the AGELACRINITID&, comprising, probably, but one known 
genus: Agelacrinites. The recognised species of this genus are 
enumerated im the annexed tabular view : 
Sub-kingdom Raniara, Class Ecutnopermars, Order Tayroma, 
Family AGELACRINITID#, Genus AGELACRINITES. 
Synopsis of Species. 
A.— Lower SILURIAN SPECIES : 
(Rays curved) : 
1. A. Buchianus, %. Forbes. 
2. A. Cincinnatiensis, Roemer. 
3. d. Dicksont, Billings. 
4. Ad. (Edrioaster) Bigsbyi, Bulings. 
(Rays straight): | 
5. A. Bohemicus, Roemer. 
6. A. Billingsii, Chapman. 
B.— Upper SrLuRIAN SPECIES : 
(Rays straight) : 
7. A. parasiticus, Hall. 
