450 F. R. Coivper Reed — Fossils from Maverfordwest. 



valve; teeth small, slender, divergent. Brachial valve with small 

 bifid cardinal process, each arm transversely grooved ; dental sockets 

 narrow, diverging at more than right angles ; low, short, rounded 

 ridge between faint adductor scars. 



Surface of valves oi'namented with one conspicuous, single, strong 

 but slender median rib, with 16-20 fine, straight, primary, radiating, 

 raised, thi-ead-like lines on each side, and between each pair 3-5 finer 

 strise or lines. A few concentric wrinklings occasionally present 

 near cardinal angles. Shell strongly punctate. 

 Dimensions. 



I. II. III. IV. 



Length ... 10-0 ... 10-5 ... 8-0 ... 14-0 mm. 



Width ... 19-5 ... 15-0 ... 12-0 ... 16-5 mm. 



Locality. — Quarry at Upper Slade. 



Horizon. — Slade Beds. 



Eemarks. — The presence of the median rib and character of the 

 surface-ornamentation distinguish this form from S. compressa, Sow., 

 from the Llandovery Beds, to which in general shape, contour, 

 and internal features it is closely allied. The variety of S. compressa 

 termed llandeiloensis by Davidson,^ from the Llandeilo Flags, has 

 the same points of difference, and in addition possesses larger 

 diductor scars in the pedicle valve. The Llandovery shell appears 

 to belong to the genus Stropheodonta, according to Hall & Clarke, 

 judging from the hinge, but the transverse crenulations are not 

 clearly visible in our Slade shell. One of our specimens, probably 

 a young individual, as it is of small size, has much produced lateral 

 wings, but in the majority of examples the cardinal angles are only 

 slightly produced, though always acutely pointed. 



Strophomena antiquata. Sow., var. (PI. XXIH, Fig. 12.) 



The peculiar lobed variety of S. antiquata, figured by Davidson ^ 

 from the Wenlock of Dudley, occurs in the Eedhill Beds of 

 Prendergast Place, Haverfordwest. In this form the pedicle valve 

 has a broad, deep, rounded sinus down the middle, with an elevated 

 rounded lobe on each side passing gradually into the somewhat 

 flattened ears. The shell is markedly transverse, being nearly twice 

 as wide as long ; the hinge-line is at the greatest width of the shell, 

 and the cardinal angles are almost rectangular, or form an angle 

 of about 75°. The diductor muscles in the pedicle valve form 

 a subquadrate or subpentagonal impression about one-third the 

 length of the valve. The Kedhill specimens, being in the condition 

 of internal casts, do not show the ornamentation of the surface, but 

 a few concentric wrinkles are traceable in one specimen near the 

 lateral angles. It seems to me a matter of doubt whether this form 

 is not specifically separable from S. antiquata, var. scabrosa, which 

 also occurs in the Ordovician of the Haverfordwest district. The 

 shape of the shell is utterly different, and the ornamentation as seen 

 in the typical Wenlock examples is completely distinct. 



1 Davidson: Mon. Silur. Foss. Brach., vol. iii, p. 316, pi. xlvi, figs. 11-14. 



2 Davidson: op. cit., p. 299, pi. xliv, fig. 3. 



