MARTESIA. 231 



ira„ji/^_PHOLADID.E, Leach. 



Genus — Martesia, Leach in H. M. D. rie Blainville, 1825. 

 (' Manuel de Malacol.,' p. 632.) 



Maetesia coNSTEiCTA (rJuIUps), 1829. Plate XXXVIII, figs. 3—10. 



1829. Pholas constricta, /. PJiilhyi. Geol. Torks.,p. 169 (p. 256, ed. 3), pi. ii, 



%. 17. 

 1850. — —A. d'Orbigny. Prodr. de Pal., vol. ii, p. 117. 



1854. — — J.Morris. Cat. Brit. Foss., ed. 2, p. 221. 



1864. — — F.J. Field and G. Campiclie. Foss. Terr. Crit. Ste. 



Croix (Mater. Pal. Suisse, ser. 4), 

 p. 26. 

 1870. — — F. Stoliczka. Palisout. ludica, Cret. Fauua S. ludia, 



p. 23 (? Martesia). 

 1900. Pholadidea constricta, A. J. Jukes-Browne. Cret. Eocks of Britain, 



vol. i, p. 470. 



Description. — Shell small, more or less elongate; anterior part short, convex, 

 rounded ; posterior part wedge-shaped. Umbones prominent, close together, 

 curved inwards and forwards. Ventral margin nearly straight. Posterior margin 

 sub-truncate, more or less rounded, somewhat oblique. Postero-dorsal margin 

 sloping ventralh'. Two narrow furrows, with corresponding internal ribs, extend 

 from the umbo to the ventral margin; the anterior furrow is rather broader and 

 less oblique than the posterior, i)ut is sometimes short or absent. An internal » 

 ridge, near the postero-dorsal margin, extends from the umbo to near the posterior 

 adductor. Anterior callus shield-shaped. Ventral margin of valves diverging 

 posteriorly, joined by a hypojdax. Metaplax elongated, divided. 



Ornamentation : on the larger part of the shell distinct, regular, concentric 

 ribs with minute transverse sei-rations. In front of the anterior furrow the ribs 

 become smaller and closer together; they ])end dorsally and unite at an angle 

 with similar ribs on the dorsal })art of the anterior end of the valve. On the 

 postero-dorsal part of the shell the ribs are less regular and less distinct. 



Measurements : 



(2) (3) (4) (.^>) 



17 . k; . 18 . 15 



9 . 9 . 10 . 9 



9.9. 10-5. 9 



(1 — 3) Speeton, (4 — 7) Folkestone. 



Affinities. — This species is less elongate than M. subcijlindrica (d'Orbigny).' 

 1 ' Pal. Franc. Terr. Crot.,' vol. iii (1845), p. 306, pi. cccxlix, figs. 5—8. 



