60 MOLLUSCA FROM THE CRAG. 



4. Modi ola costulata, Risso. Tab. VIII, fig. 6. 



Modiolus costulatus. Risso. Hist. Nat. de l'Europ. Merid., t. iv, p. 324, pi. xi, fig. 165, 



1826, non bene. 

 Modiola costulata. Phil. En. Moll. Sic, vol. i, p. 70, t. 5, fig. 11, 1836. 

 _ — Id. vol. ii, p. 50, t. 15, fig. 10, 1844. 



— Petagnje. (Scacchi) sec. Phil. En. Moll. Sic, vol. ii, p. 51. 



— costulata. Webb and Bertholet. Nat. Hist, des lies Canaries, p. 103, pi. 7, B, 



figs. 23, 25, 1842. 



— — Jeffreys. An. Nat. Hist., vol. xix, p. 313. 



— cylindroides. (S. Wood. Catalogue, 1840. 



Crenella costulata. Forb. and Hani. Hist. Brit. Moll., vol. ii, p. 205, pi. 45, fig. 1, 1849. 



Spec. Char. Testa minutd, oblongd, subcylindricd, antice angustata et ultra apicem 

 productd, medio Icevi ; in utroque latere costato-striatd. 



Shell small, oblong, subcylindrical, anterior side somewhat contracted, extending 

 beyond the umbo, middle smooth, with large costated striae upon both sides. 



Longest diameter, J- ths of an inch. Shortest, f ths. 



Locality. Cor. Crag, Sutton. 



Red Crag, Walton Naze. 



Only one specimen in my cabinet has been obtained from the older or Coralline 

 Crag Formation; but in the Red Crag at Walton it does not appeal* to be at all scarce, 

 at least a couple of dozen have fallen to my lot, and in them a considerable range in 

 variation may be detected. 



Our shell appears to agree with the figure and description of M. costulata, in the 

 first vol. of Philippi, which that author, in his second volume, has assigned to another 

 species : amongst my specimens also are forms corresponding with what he con- 

 siders to be specifically distinct, and they are therefore both introduced among the 

 synonyma, as I am unable to separate into two species those which are found in the 

 Crag ; if, however, there be in the recent shells characters sufficient to justify a 

 specific distinction, both forms seem to have been present in the seas that deposited 

 the Red Crag, but from what is exhibited in the fossils, they may be fairly included in 

 one species. 



There can be no mistake in regarding this as distinct from either M. discrepans 

 or M. marmorata, from both of which it differs in being more cylindrical, with 

 also a greater curvature in the ventral margin. It is an elegantly-formed shell, 

 the anterior side slightly projects beyond the umbo, somewhat tumid, with a rounded 

 angularity crossing the shell diagonally from the beaks to the posterior part of the 

 ventral margin, the anterior side is rounded, and deeply striated or ridged with about 

 ten or twelve small ribs ; the middle is plain, or only marked by lines of growth, 

 while the greater half of the shell on the posterior side is covered with striae in a 

 radiating manner, these are so conspicuous at the margin as to produce somewhat 

 large and distinct crenulations on the inner edge, most conspicuous a little behind the 



