﻿ATRYPA. 



57 



Var. aspera, Sohloth. PI. X, figs. 5 — 8. 



TEREBRATULA ASPERA, Schlotheim. Leonhard'sTaschcnbuch, p. 74, tab. i, fig. 7, 1813; 



and Petrf., Part I, 263, Part II, 68, tab. xviii, fig. 3. 

 Atrypa aspera, Dahnan. Uppstallring och Beskrifning af de i Sverige funne Tere- 

 bratuliter ; Kongl. Vetenskaps Academiens Handlingar f ur an 1827, 

 p. 128, tab. iv, fig. 3. 

 Terebratula aspera, Def. Diet, liii, p. 164, 1828. 



— reticularis, Bronn (in part). Index Palseontologicus, p. 1249, 1848. 

 Atrypa squamosa, Soiv. Trans. Geol. Soc., 2nd series, vol. v, pi. lvii, fig. 1. 

 Terebratula (Atrypa) aspera, Phillips. Palaeozoic Fossils of Cornwall, Devon, and 



West Somerset, p. 81, pi. xxxiii, fig. 114, 1841. 

 Spiriferina reticularis, var. aspera, M'Coy. British Palaeozoic Fossils, p. 379. 



Although I quite admit with Prof. Phillips that the distinctiveness of some specimens 

 of this shell, even of equal size when compared to typical ones of A. reticularis or prisca, is 

 great, still as the difference, which consists in the paucity of ribs in extreme forms of 

 Aspera, and the many smaller ones in Reticularis, is not a persistent character, to the 

 generality of specimens of both, each extreme being connected and linked together by 

 every gradation in shape and number of ribs, I dare not venture to look upon A. aspera 

 as more than a well-marked variety of A. reticularis. This view has also been taken by 

 Bronn, M'Coy, and several other palaeontologists. A. aspera is always found in the same 

 beds and localities where A. reticularis occurs and abounds, and possesses similar external 

 shapes. 



The only difference or character I can perceive by which this variety may be 

 distinguished is when its ribs are few in number, and consequently proportion ably larger, 

 the concentric laminse being in such specimens wider apart, but similar in character to 

 those of A. reticularis. Schlotheim's original figure of A. aspera is just one of those 

 intermediate links connecting the two, while those given by Phillips are extreme conditions 

 of the shell under description. Phillips describes A. aspera as " generally wider than 

 long, lenticular, with slightly prominent beak, minutely perforated below" (the foramen 

 being almost surrounded by a well defined deltidium, a small flattened space usually 

 intervening between the beak-ridges and the hinge-line, which distinguishes it again a 

 little from A. reticularis, although I have seen some specimens of the Linnsean shell 

 showing the same character), " front raised in a gentle curve, surface radiated with from 

 twelve to twenty broad rounded ribs" (which increase in number at variable distances 

 from the beaks, as in A. reticularis) " crossed by projecting concentric fringed laminae 

 of growth." 1 



1 When describing Spiriferina reticularis, var. (I aspera (Schloth. sp.), Prof. M'Coy observes : 

 " This variety, which is at first sight so extremely different from the ordinary Silurian type, by its few very 



H 



