F. R. Cowper Reed — Fossils from Haverfordwest. 493- 



Arca [Palmarca] Turnbulli, sp. nov. 

 Whitella (?) inutilis, sp. nov. 

 Ambonyehia cf . raiiata, Hall. 

 Modiolopsis Martini, sp. nov. 



,, suhgradata, sp. nov. 



,, sp. indet. 

 Goniojjhora cf. cymbceformis, Sow. 



Okthodksma semiradiata, sp. nov. (PI. XXIV, Figs. 8, 9, 

 10, 10a.) 



Description. — Shell elongate-oval, narrow, about three times a& 

 long as high, gaping slightly at both ends ; inferior and superior 

 margins subparallel ; beaks small, not prominent, scarcely rising 

 above hinge-line, directed forwards, situated at about one-fourth or 

 one-fifth the length of the shell from the anterior end, with small 

 indistinctly defined lunulate area in front of them ; anterior end of 

 shell short, narrowed, acutely rounded ; posterior end obliquely 

 truncated with inferior angle subacutely rounded ; cardinal margin 

 straight, about one-half to two-thirds the length of the shell ; 

 inferior margin gently arcuate, curving up sharply in front. Valves 

 compressed, very slightly convex, with weak, rounded, umbonal 

 ridge running obliquely backward from beak towards postero- 

 inferior angle, before reaching which it becomes obsolete ; surface 

 of valve flattened above umbonal ridge ; no distinct medial depression 

 present. Surface of valves ornamented with sharp, concentric, sub- 

 equal lines and strige, well marked in front of umbonal ridge, behind 

 which they are nearly obsolete ; umbonal ridge and post-umbonal 

 surface marked with fine, low, closely placed, rounded radii, most 

 distinct near inferior angle. Anterior adductor impression sub- 

 marginal, ovate, more or less distinct ; posterior adductor and pallial 

 impression not visible. Shell apparently thin. 



Dimensions. 



I. II. III. IV. V. 



Length 26-5 32-5 23-5 19-0 29-Omm. 



Height (at beak) 6-5 12-5 8-5 4-5 7-5 mm. 



Distance of beak from anterior end 6-0 — — — — 



Horizon and Locality. — Slade Beds : roadside near St. Martin's 

 Cemetery, Haverfordwest. 



Eemarks. — This species is fairly common in the Slade Beds, near 

 St. Martin's Cemetery, Haverfordwest, a locality at which many 

 Lamellibranchs are found. The specimens are frequently somewhat 

 distorted and crushed, and suggest a thin delicate shell. The true 

 generic position of this shell is somewhat doubtful, since we are 

 ignorant of its hinge-characters, and since the classification and nomen- 

 clature of the Lower Palasozoic Lamellibranchs is in a notoriously 

 unsatisfactory and unsettled condition. Ulrich^ has recently revised 

 the members of this group occurring in the Ordovician beds of 

 Minnesota, but his diagnoses are not always easy to apply to the 



1 Ulrich, Lower Siliu-. Lamell. Minnesota: Geol. Surv. Minnes., vol. iii, pt. 1 

 1895, pp. 475-628. 



