92 PALEONTOLOGY OF NEW YORK. 



SoBOENCs 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. cit., 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' Spin/era 

 (= 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 expansions! 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, fpr 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 lamellse 

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



* McCoT afterwards refeireil the species to the genus Athyris : British Palaeozoic Fossils, p. 486. 1865. 

 t See Datidsoh's superb fif^res in Carboniferous Brachiopoda, pi. xvi., figs. 7, 8. 

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



