92 PALEONTOLOGY OF NEW YORK. 



Subgenus ACTINOCONCHUS, McCoy. 1844. 



In the same work that contained the original description of Athyris, McCoy 

 proposed the above term for a shell which he described as Actinoconchus 

 paradoxus. 



" General Characteristics. — Shell globose ; the margin of both valves greatly 

 extended, forming a flat, circular, striated disc ; spiral appendages as in Athy- 

 ris."— {Op. cil, p. 149.) 



Its affinities with Athyris were evident to the author, and later writers have 

 regarded it simply as a synonym for that term. The Actinoconchus paradoxus 

 was subsequently shown by Davidson to be the same shell as Phillips' Spirifera 

 (^Athyris) planosulcata (1836), which McCoy had himself identified among the 

 Carboniferous fossils of Ireland from desquamated specimens (p. 148 ).* 



There seem to be excellent reasons for reinstating this term in its original 

 application, as Athyris planosulcata is a strongly individualized species which 

 may well serve as the type of a group. 



It is characterized by the extravagant development of the concentric lamel- 

 lar expansionsf which are striated radially by distant sulci " about half a line 

 apart" (Davidson). These expansions appear to be actually fine, tubular spines 

 connected by, or imbedded in a tenuous calcareous plate. The interior of the 

 pedicle-valve bears a median septum which traverses the pedicle-cavity and 

 half the length of the shell; also two strong dental plates which are continued 

 forward, slightly diverging, for more than one-half the length of the septum. 

 Mr. Davidson has given elaborate illustrations of the spirals and loop of this 

 species, from preparations by the Rev. Norman Glass,| and from them it appears 

 that the latter organ, the loop, has essentially the same conformation as in 

 Cliothyris pectinifera, though it is placed further forward (see Silurian Supple- 

 ment, p. 98, fig. 1.). The saddle of the loop is neither divided nor pectinated, 

 while the spiral ribbon bears short spinules " on the edge and face of the lamellae 

 fronting the sides of the shell " (Davidson). Athyris planosulcata is a species 



* McCoy afterwards referred the species to the grenus Athyris : British PaL-eozoic Fossils, p. 436. 1855. 

 t See Davidson's superb figures in Carboniferous Brachiopoda, pi. xvi., figs. 7, 8. 

 i Supplement to British Silurian Brachiopoda, p. 98, figs. 1, 2, pi. iv, figs. 14-19. 



