﻿Vol. 64.] BRACHIOPOD HOJiKEOMORPHY : ' SPIlUFEll GLABEIt! 



3. BRACHlorOD HOMCEOMOEPHY : ' SP/li/FEIi GLABEIi.' 



By S. 8. BucKMAN, r.G.S. (Read December 4th, 1907.) 



It is easy, but it is very dangerous, to group together under one 

 name a series of shells of similar apj^earance, especially when they 

 are in the smooth catagenetic stage ; because this smooth stage may 

 have been attained by the loss of different distinctive features, 

 pointing to poly genetic origins. An instructive case in this respect 

 is found in the series of forms called Sjnrifer glaber. 



As Spirifera c/Iahra, Davidson ^ figured a series of shells which do 

 not all agree in being smooth ; for, though most of them are smooth, 

 some are radially costate. And they do not agree in shape: some 

 have a pronounced mesial fold, others hardly any ; some are very 

 transverse, others are narrow. Then in his synonymy he com- 

 bined under this name many species of other authors : Sj). obtusuSy 

 Sp. ohlatus, Sowerby, JSp. lincjitifera, Sp). symmetrica y Sp. decora^ 

 Phillips, Sp. Icevigatus, von Buch. 



Of late years this glaher-Beiie^ of the Carboniferous, and certain 

 smooth Spiriferids of the Devonian, have been ranged in M'Coy's 

 genus Martinia. 



A somewhat similar series of Spiriferids is grouped under Reti- 

 cularia, M'Coy : their distinguishing character is a reticulate 

 surface. Davidson makes the principal species Spirifera lineata 

 (Martin), and ranges under it Terehratula (?) imbricata, Sowerby, 

 Spirifera eUiptica and Sp. mesoloba, Phillips, JReticularia reticulata 

 and Martinia stringocephahides, M'Coy. 



In Reticularia the ornament is in the catagenetic stage, de- 

 creasing in intensity; so that partially or wholly smooth Reticularioe 

 are to be expected. 



There is good evidence that several of the forms ranged under 

 Spirifera glabra are Reticularice, more or less smooth. Thus the 

 Sp. obtusus, Sowerby, is a Reticularia. Examination of the type- 

 specimen shows faint but distinct traces of a reticulate youth 

 developing into a smooth adult ; and in the broken beak may be 

 seen the dental plates. Sp. obtusus is allied to Sp. eUiptica^ 

 Phillips ; but perhaps it is a smooth development of R. reticulata, 

 M'Coy : at any rate, it must be removed from the glaber-series and 

 be classed as Reticularia obtusa. 



Accelerated development along the same line should produce a 

 wholly smooth shell, and the only evidence that it was a Reticularia 

 would be the possession of dental plates. There are such smooth 

 forms called Sp. glaber, which show dental plates ; they arc like 

 the fossil depicted by Davidson in his pi. xii, fig. 1 : in shape and 

 degree of mesial fold they look just like reduced editions of 

 R. obtusa. It may be that this species is the one named by Brown 



^ ' Monogr. Carb. Brachiop.' (Pal{3eont, Soe, 1858-63) pis. xi & xii. Other 

 references to Davidson are to the same work. 



