a 



330 DR. A. M. DAVIES AND MR. J. PRINGLE ON [June 1913, 



in diameter. It agrees with 0. liolcleni in the central position of 

 the umbo, but differs in the more nearly circular outline, the ratio 

 of length to breadth being 8 : 7 instead of 5 : 4. It is not quite so 



nearly circular as 0. davidsoni 

 Pig. 2. — Orbiculoidea off. holdeni Moore. A noticeable feature 

 Tate (431-432 feet). in the best-preserved specimen 



is the somewhat inflated apical 

 region, as shown in the profile 

 (fig. 2 b). 



This shell may perhaps be 

 identical with the form men- 

 tioned but not named by 

 Davidson (' Brit. Foss. Brach.' 

 Monogr. Pal. Soc. vol. v, 



[a = Brachial valve, external view. P- 2 " 9 )> fonn & *¥ Brodie in 



b — The same in profile. Both x 8.] the Lower Lias (Lima beds 



and shales, that is, lowest 

 Sinemurian) of the Vale of Gloucester and Harbury. 



Charmouthian — jamesoni or valdani zone, at 431-432 feet, 

 Calvert Boring. Coll. A. M. Davies. 



Obolella (?) aff. salteri Holl. (Fig. 3, p. 331.) 



1865. Obolella salteri Holl, Q. J. G. S. vol. xxi, pp. 101, 102 & fig. 9. 



1866. Obolella salteri Davidson, ' Brit. Silur. Brach.' Monogr. Pal. Soc. pt. vii, 



No. 1, p. 61 & pi. iv, figs. 28-29. 

 1902. Obolella (?) salteri Matley, Q. J. G. S. vol. lviii, pp. 138-140 & figs. 3-6. 



Form broadly ovate; length = 6*25 mm., greatest breadth the 

 same or very slightly less, at 3 mm. from the umbo. Pedicle and 

 brachial valves closely similar, the former having the umbo 

 slightly more pointed. 



Surface ornamented with fine concentric lines, which appear to 

 be the only markings on the outer surface, but the outer shell- 

 layer is only preserved in fragments ; where it is removed, the 

 exterior of the inner layer shows, crossing the fine concentric 

 lines, very delicate radial lines, in addition to which there are much 

 coarser and rather indefinite radial corrugations, four or more in 

 number, appearing at about 1 mm. from the umbo, dying away at 

 about 3 mm. from it, and occupying a breadth of about 0'75 mm. 

 on each side of the middle line. There are also seen, on the same 

 surface, a number of minute pustules, scattered in an irregular 

 manner over an area somewhat larger than that occupied by the 

 corrugations. Dr. Matlej-, to whom the specimens were shown, 

 suggested that these might be the bases of spines, but no evidence 

 of spines could be found. The irregularity of these pustules, and 

 the fact that each one is surrounded by an aureole in which the 

 brown colour of the shell is replaced by white, suggested the idea 

 that they might be due to minute boring organisms. 



Pedicle- and brachial valves in a few cases occur together, some- 

 what displaced from the natural position. In the majority of cases 

 only the outer surface of a single valve can be seen ; and in nearly 

 every case this is the brachial valve, but one unquestionable 



