﻿Vol. 64.] IN THE CAEBONIFEROUS ROCKS AT LOUGHSHINNY. 469 



This species agrees with Martinia ovalis in the plan of ribbing, 

 but differs markedly in form and length of hinge-line. 



Towards the end of Avonian time, the gens of Martinia glabra 

 gave birth to a large number of variants, most of which are smooth 

 and differ only in form, although this difference is often strongly 

 marked. 



Martinia ovalis and the species here described are ribbed devia- 

 tions from the same gens, exhibitiug reversion towards the earliest- 

 known Martinia^ namely M. cf. linguifera, of which a very few 

 examples have been found in Z., and y of the South-Wesfcern 

 Province. 



Martinia ovaliglahra ranges, in the Rush-Skerries sequence, 

 through the beds containing Posidonomya^ and is an important zonal 

 fossil. 



Mr. J. T. Stobbs has collected some beautiful examples from the 

 highest Avonian of the North Wales area. 



Reticularia. 



Reticflaeia lineata (Mart.). 



= Eeticularia imhricata (Sow.) & (Phill.). 



= Spirifera lineafa Ya,i\ reticulata, Davidson (pars), pi. xiii, figs. 11 & 12. 



The dental plates are sub-parallel and conspicuous ; the ornament 

 consists of broad imbricating bands bearing broad rib-like spines. 

 Specimens are met with, somewhat rarely, in the Dihunophyllum- 

 Limestone and in Lower P. 



RETICULATilA LINEATA (DaV.). 



= Spirijera lineata, Davidson {pars), pi. xiii, figs. 5, 8, & 10. 



Small globose form with suppressed ornament. Dental plates 

 markedly divergent, and therefore approximate to the inner wall 

 of the umbonal region ; subsequent shell-deposit frequently includes 

 and conceals them within the thickened wall. 



Specimens are common in the Dibunophyllum-IAmestoiie and in 

 Lower P ; extremely abundant at the ' Knoll' level in the Western 

 Midlands and Yorkshire ; and not uncommon in D„ of the South- 

 western Province. 



Athtrids. 

 Athyris (Actinoconchus ?). 



Athyris cf. PLANOSULCATA (Phillips). (PL L, fig. 6.) 



= Athyris pla7iosulcata, Davidson, pi. 11, fig. 12. 



This form appears to be a variant from Athyris eccpansa (Phillips) ; 

 it is characterized by the circular outline and by the strong develop- 

 ment of radial ridges on the cast. Specimens are not uncommon 

 in Lower P. 



