572 MR. J. A. DOTJGIAS ON THE [Nov. I9O9, 



' Monograph of the British Fossil Brachiopods ' vol. ii, is represented 

 by fig. 7 in pi. i {Terebratula hastata). 



2. In D 1 occurs a form with a narrow wedge-shaped anterior 

 margin, and very convex valves without depressions, which' 

 resembles Dielasma itaitubense, de Kon. (oj>. cit. pi. v, figs. 4 & 5). 

 This is probably closely related to D.ficus (M'Coy). 



3. The most abundant form in D, however, is similar to that 

 figured by Davidson (op. cit. pi. i, fig. 12) as Terebratula virgoides, 

 M'Coy. 



It would appear then, from a brief study of the history of the 

 genus, that D. virgoides (M'Coy) and D. jicus (M'Coy), which 

 Davidson includes as varieties of I), hastatum (Sow.), must rank as 

 distinct species. 



Athyris. 



Al'HYEIS GLABRISTRTA (Phill.). (PI. XXVI, fig. 2.) 



The typical form of this shell, as described and figured by 

 Phillips in the ' Geology of Yorkshire ' pt. ii, p. 220 & pi. x, fig. 19, 

 and by Davidson, under the name of Athyris royssii, in his 

 ' British Possil Brachiopoda ' (vol. ii, pi. xviii, figs. 1-11), is 

 enormously abundant in the Syringoihyris Zone of County Clare, 

 though somewhat scarce in the beds below. This species exhibits 

 a remarkable variation in growth, and hardly any two specimens 

 obtained from this level have the same relative dimensions. 



The ratio of length to breadth in three specimens taken at 

 random was found to be 4 : 7, 4 : 10, and 4 : 13. 



The young shell is depressed, with a slight median fold. In 

 some cases, further growth is chiefly directed towards increasing 

 the depth of the shell, resulting in a deep form with rounded fold ; 

 in others, there is little increase in depth : the shell remains 

 flattened, and may become extremely transverse ; the fold in this 

 type is often very prominent, with steep sides. There can be little 

 doubt that this form is identical with Athyris ingens of L. Gr. 

 de Koninck, which characterizes the Waulsortian Phase of Belgium 

 (op. cit. pi. xx, figs. 1-10). In comparing this species with other 

 Athyrids the author lays stress on the absence of ornamentation : — 



' . . . . l'auteur [Davidson] a du admettre que les specimens representes avaient 

 perdu leurs ornements pendant la fossilisation, ce qui ne parait pas d'accord 

 avec leur parfait etat de conservation.' (Pp. 83-84.) 



The preservation of fringe-like expansions on the shell is 

 dependent largely on the mode of fossilization, and their apparent 

 absence from the Belgian type of A. ingens cannot be taken as 

 proof of their non-existence. Many specimens that I have collected 

 from County Clare present, at first sight, a perfectly smooth surface 

 which shows little trace of ornamentation ; but, on grinding and 

 polishing the matrix in which they are embedded, the presence of 

 fringes can always be determined. 



