14 BRITISH TERTIARY BRACHIOPODA. 



Mr. S. Wood discovered a few young specimens, noticed in his Catalogue under the name 

 of T. gervillei ? The question now is, whether T. caput serpentis really occurs lower down 

 in the series, as some persons seem disposed to believe, from similarly shaped shells being 

 found in almost all the series of tertiary deposits, as well as in those of the cretaceous 

 period. We have compared with great care a number of these, and must confess that, in 

 many cases, the variations are so trifling, that we find them in general reproduced on 

 various specimens of the living type. It is only on adult shells, where all the characters are 

 developed, that a positive determination as to specific difference can be established, great 

 similarity existing in the young state of this genus. We believe, however, that there are 

 some differences, which, though slight, may allow us perhaps to establish a few species and 

 varieties, although we do not consider the subject as yet satisfactorily decided. Professor 

 Forbes, in whose judgment I have great confidence, inclines to believe, that the recent 

 type is really found lower down, both in the tertiary and cretaceous period, but for the 

 present I have been unable to satisfy myself that such is truly the case, although it may be 

 so. It is, however, certain, that too many species have been proposed in the genus, which 

 will be referred to in their proper places. 



6. Terebratulina striatula, Soto., Sp. Plate I, figs. 16, 16 al . 



Terebratula striatula, Sow. (Partim non T. striatula, Mantell,) 1829, vol. vi, 



p. 69, tab. 536, fig. 5, non figs. 3, 4. 

 — — Morris. (Partim) 1843. Catalogue. 



Diagnosis. Shell of a rounded oval or irregularly pentagonal shape, longer than wide; 

 valves convex and compressed; beak not much produced, truncated by a moderately sized 

 foramen, principally excavated out of the substance of the beak, and completed by the 

 umbo and two small lateral obsolete deltideal plates ; no distinct area or beak ridges ; 

 hinge lines circular ; auricles small, often almost indistinct ; valves ornamented by a great 

 variety of minute striae or costae of unequal width, sometimes bifurcating, but more often 

 augmenting by the intercallation of smaller costae appearing at different distances from the 

 umbo and beak, and extending to the front. Margin line slightly flexuous. Loop short, 

 anneliform. Length 10, width 8, depth 4 lines. 



Obs. Although the distinctions between this shell and the recent caput serpentis 

 are not very great, still we think them sufficient to authorise its separation. Both young 

 and adult specimens of the recent species just mentioned seem in general more convex, and 

 tapering at the beak than in the London clay species, which is wider and more circular at 

 the beak, the valves being likewise much more compressed, and the margin line less 

 sinuous, nor do we find that mesial longitudinal depression so often visible in the cretaceous 

 T. striata; the striae which ornament the valves is so variable in number, as well as in 

 dimensions, that they cannot serve as a distinguishing character; they increase in number 

 rapidly at a short distance from the beak and umbo, much more by intercalation than 



