﻿RETZIA. 



S7 



subtilita, Hall, the material then at my command not being sufficient to enable me to 

 determine positively whether it was a true Terebratula or an Athyris. Many excellent 

 examples having subsequently turned up, I was able to assure myself that it was with the 

 last-named genus that Professor Hall's species must be located, and now hasten to place it 

 among its congeners. I also assured myself that the shell described by Professor M'Coy, 

 in his work on ' British Palaeozoic Fossils,' under the denomination of Athyris gregaria, 

 belonged to Professor Hall's A. subtilita, and not to the shell which the same author 

 had originally so designated in his ' Synopsis of the Characters of Irish Carboniferous 

 Fossils/ and to which the term gregaria belongs. 



Athyris subtilita occurs also in the Carboniferous limestone of Tournay in Belgium, 

 and fig. 1, pi. xx, of Professor de Koninck's work on 1 Belgian Carboniferous Fossils,' is 

 referable to this species. At p. 714, of his 'Iowa Report,' Professor Hall states "that 

 T. subtilita has a very wide range, being known in the eastern Ohio, Indiana, Illinois, 

 Iowa, Missouri, Kansas, Nebraska, and Pecos village, in New Mexico." The British 

 localities have been already mentioned. 



Retzia radialis, Phillips. Plate XVII, figs. 19 — 21. 



Terebratula radialis, Phillips. Geology of Yorkshire, vol. ii, p. 223, pi. xii, figs. 40, 41, 

 1886. 



Terebratula mantice, De Koninck. Animaux fossiles Carbonifere de la Belgique, p. 



287, pi. xix, fig. 4, a, b, c, d, 1843 (not T. mantice of Sowerby). 

 Atrypa radialis, M'Coy. Synopsis of the Characters of the Carboniferous Fossils of 



Ireland, p. 156, 1844. 

 Retzia radialis, Morris. A Catalogue of British Fossils, p. 145, 1854. 

 Spirigerina (?) radialis, M'Coy. British Palaeozoic Fossils, p. 438, 1855. 



Spec. Char. Circular or longitudinally ovate ; valves almost equally and moderately 

 convex, without fold or sinus; margin of valves almost straight. Each valve is ornamented 

 by about twenty small, rounded, radiating ribs, of which the central one in the dorsal valve 

 is at times the largest, and to which, in the ventral valve, corresponds a deeper sulcus ; 

 but this difference is not always apparent, and in some specimens the dorsal valve appears 

 for some distance divided by a median depression, from which arises a central rib. The 

 beak is more or less produced and truncated by a circular foramen, which is more or less 

 separated from the hinge-line by a small triangular area. Shell-structure punctate. 

 Interiorly, two spiral appendages, with their extremities directed outwards, exist for the 

 support of the oral arms. Two examples have measured — 



Length 5, width 5, depth 3 lines. 

 4 4 3 



Obs. This little Betzia was in 1843 mistaken by Professor de Koninck for Sowerby 's 

 T. mantice, but the distinguished Belgian palaeontologist subsequently discovered and 



