Vol. 62.] LIMESTONE OF THE MENDIP AREA. 375 



pi. xvii, figs. 3 & 3 a, of Davidson's monograph, but some specimens 

 approach pi. xvi, fig. 17 in transversity. 



I am unable to distinguish the specimens occurring in the 

 Dibunophyllum-Zone from those in the Syringothyris- and Semi- 

 nula-Zones, and I am ignorant of the nature of the shell-expansions, 

 which are not preserved in any of my specimens. The line con- 

 centric ornamentation of the shell, however, renders it very unlikely 

 that the expansions were strong lamellae. 



Athyris cf. plan o sulcata (Phil.), Davidson. 



The common form in the Lower Seminula-Zone of the Mendip 

 area is closely represented, in general shape, by pi. xvi, figs. 4-4 6 

 of Davidson's 4 Monogr. Brit. Foss. Brachiop.' (Palaeont. Soc.) 

 vol. ii (1858-63). But, although I have no direct evidence as to 

 the nature of the shell-expansions in our form, the fine concentric 

 ornamentation of the valves renders it almost certain that these 

 expansions were not strongly lamellar, as they are in the typical 

 form of Athyris (Actinoconchus) planosulcata. 



Beticularia. 

 Heticularia cf. reticulata, M'Coy. 



= Beticularia aff. lineata, Vaughan, Quart. Journ. Geol. Soc. vol. lxi 



(1905) p. 299. 

 Compare M'Coy, ' Syn. Carb. Liraest. Foss. Ireland ' 1844, p. 143 & 



pi. xix, fig. 15, aud Davidson, ' Monogr. Brit. Foss. Brachiop.' (Palasont, 



Soc.) vol. ii (1858-63) pi. xiii, figs. 13 & 13 a. {Spirifera lineata, vai\ 



reticulata.) 



The Mendip form closely resembles M'Coy's type-figure, though 

 an average specimen from the Mendips is larger than the type. 

 The strong dental plates, combined with the well-developed area 

 and the reticulate structure of the test, characterize our form as a 

 typical Reticularia. 



This form undergoes little mutational change throughout its 

 long range in the Mendip sequence ; but it is important, as being an 

 essentially-Clevedonian fossil. 



Spirifer. 



Spirifer cf. bisulcatus, J. Sow. 



Specimens occurring commonly in the Syrinc/othyris-Zone, and 

 more rarely in the Lower JSemi7iula-Zone, of the Mendip area show 

 a general resemblance to the type of Spirifer bisulcatus, as figured 

 in Davidson's 'Monogr. Brit. Foss. Brachiop.' (Palaeont. Soc.) vol. ii. 

 (1858-63) pi. vi, figs. 6-9 ; poorness of material prohibits a detailed 

 description of our form. 



The few specimens that I have obtained from the Upper 



