BRACHIOPODA. 93 



which has a wide distribution through the lower and upper Carboniferous of 

 England, Ireland and Belgium. 



Subgenus SEMINULA, McCoy. 1844. 



This is another term proposed in the " Synopsis of the Carlwniferous Fossils 

 of Ireland," which has been absorbed into the genus Athyris by later writers. 

 On page 150 of his work, McCoy mentions Seminula as " a genus formed for 

 the reception of those little species which have a minute perforation but want 

 the deltidium," and further, on page 158, describes the genus as follows: 



" General Characteristics. — Shell small, subpentagonal ; smooth or slightly 

 plaited at the margin ; beak of the dorsal valve small, with a minute perfora- 

 tion; no deltidium. 



" The species of this genus are all small ; the margin frequently indented, 

 but no distinct plaits on the surface ; the outline is usually more or less pent- 

 agonal ; the beak has a very minute foramen for the passage of the muscle of 

 attachment, but there is no deltidium separating the foramen from the hinge. 



" The genus is peculiar to the Palaeozoic rocks." 



In this place the author described three species, the first of which, Seminula 

 pentahedra, Phillips (sp.), may be taken as the type in absence of any specified 

 typical species. Phillips' species has been shown to be synonymous with Spir- 

 ifer ambiguus, Sowerby, and is antedated by it. The other forms referred, in 

 the work cited and subsequently, to Seminula by McCoy, have been shown by 

 Davidson to be not congeneric with .S. {Athyris) ambigua. No generic import- 

 ance can now be given to the apparent absence of the deltidium in this shell ; 

 it is simply concealed as in many other Athyres by the incurvature of the 

 beak. Mr. Davidson has described and elaborately figured the Athyris am- 

 bigua* and from his work, with the aid of a series of specimens from the Car- 

 boniferous limestone of Great Britain, f it appears that the shell has certain 

 characters which do not permit its easy association with the other subdivisions 

 of Athyris. The smooth exterior of the species, its subpentahedral form and 



* Carboniferous Brachiopoda, p. 77, pi. xv, figs. 16-22 ; pi. xvii, figs. 11-14. 1858. 



t For some of which we have been indebted to Prof. John Young, of the Hunteriaii Museum, Glasgow. 



