Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/242

194 194 J. S. GARDNER ON BRITISH CRETACEOUS PATELLID.E ETC.

nor the striae are regularly equidistant ; the shell near the base possesses short oblique striae (fig. 11 a).

This shell differs from T. tenuicosta in being more regular and elevated— and by its ribbing, which is more uniform, closer, and most delicately tuberculated. It was found by Mr. Meyer in the Folkestone beds of the Lower Greensands at Shanklin.

The specimen has apparently a perforated apex, and might at first sight be regarded as a Fissurella ; but even the most careful exami- nation leaves it doubtful whether the perforation is or is not due to accidental abrasion ; but the ornamentation, consisting of tubercu- lated striae, is so characteristic of Tectum, and so different from that of Fissurella, which is almost invariably cancellated, that there can be practically little doubt as to which family it belongs to. Fissu- rella is still unknown from British Cretaceous rocks.

Tecttjea plana, sp. nov. Lower Greensand. PI. YIII. figs. 27-29.

Shell minute, laterally compressed, very elongated, cup-shaped ; apex recurved ; posterior region without ribs, but with lines of growth ; surface smooth, but under the microscope rugose or wea- thered. L. 4 millims., b. 2 millims., ht. 2 millims. Unique. Found, by Mr. Meyer, at East Shalford.

The shell could with equal probability be assigned to the Lepetidae, some of which it much resembles ; but there are also smooth forms of Tectum still existing.

Tecttjea tentticosta, D'Orb. Gault. PL VII. figs. 19, 20.

Shell oval, depressed, thin ; apex acute, subcentral, or i anterior ; sculpture fine, radiating, irregular ribs, almost absent on the ante- rior region, crossed by still finer striae, and occasional lines of growth. The cast is smooth.

This shell seems to characterize the Gault, where it is not un- common. Sowerby, ' Min. Conch.', figures a cast of this shell from Folkestone, together with a Lias cast, as Patella Icevis. Michelin, in 1834, figured the species in the ' Memoires Soc. GeoL' vol. iii. pi. 12. fig. 2. D'Orbigny describes it fully, with figures, in the 4 Paleont. Franc.' Pictet and Iloux have described it as Acmcea gaultina, distinguishing this form from T. tenuicosta " par son angle apicial plus ouvert, et par la position plus anterieure du sommet."

There is little doubt that some smooth limpet-like casts from the Cambridge Greensand are of this species. A rather larger specimen than the average is figured (PI. VII. fig. 20). It also occurs at Devizes.

Amongst living shells, T. tenuicosta most resembles T. testudinalis, Mull., Greenland, and T. Candeana, D'Orb., from St. Vincent, both of which are extremely variable in height.

Tectura tenetstriata, Seeley. Gault. PI. VII. fig. 18.

Minute, thin, higher than the last species, very finely striated. The specimen, still unique, is in the Cambridge Museum. It was