TROCHUS STRIGOSUS. 89 



the twist in a thread of cotton wound upon a cone. For this reason the two 

 are classed as one species, fig. L5 being var. a and fig. L6 being var. (5. 



Distribution and Relations. — Besides the two specimens from Scarborough, 

 the species may possibly occur at Shipton-on-Cherwell. At Scarborough it is 

 associated in the same bed with T. subglaber, which, so far as the ornaments go, 

 might be taken as a third of the series of still finer threads, but there are other 

 differences with regard to T. monilitectits with which one of these varieties was 

 temporarily united by Hudleston : the position of the thickest spirals is reversed, 

 while the base of the present form is entirely covered by the spiral lines. The 

 species is closely related to the much larger shell, T. pietti, Desk 



Trochus subglaber, Hudleston. Plate VIII, fig. 17. 



1885. Trochus subglaber, Hudleston, Geol. Mag. [8], vol. ii, p. 125, pi. iii, fig. 6. 



Type. — "Height, 13 mm.; spiral angle, 52°. Shell small, conical; imperforate 

 spire consists of six or seven whorls, increasing pretty regularly. Suture close, but 

 very distinct. Anterior of each whorl slightly tumid, posterior area slightly 

 constricted. The ornaments consist of fine spiral striae, very numerous, and some- 

 what closer together in the anterior than in the posterior region. These striae are 

 decussated by backward, sloping, transverse striae, which scarcely reach the 

 anterior margin. Base flat. . . ." The cross striae are too feeble to cut up the 

 spaces between the spiral striae into knobs. The latter spirals are closer together 

 on the last whorl ; they are too fine to be counted. Further development shows 

 that the base is convex and non-umbilicated, but there are no signs of any spiral 

 lines. From Scarborough. In the Sedgwick Museum. 



Distribution and Relations. — The specimen is unique. It is evidently a very 

 close relation to T. duplicans, but it grows to a larger size. The cross striae are 

 more in evidence posteriorly than the spirals themselves, and are not indicated 

 only by cutting them, while the base seems to be free from striae. 



Trochus strigosus, Lycett. Plate VIII, fig. 18. 



1863. Trochus strigosus, Lycett, Suppl. Great Ool. Mollusca (Pal. Soc), p. 29, pi. xlv, fig. 12. 

 1885. — Hudleston, Geol. Mag. [3], vol. ii, p. 124, pi. iii, fig. 3 (not fig. 4). 



1885. Trochus scarburgensis, Hudleston, ibid., pi. iii, fig. 2. 



Type. — " Shell elevated, conical, transversely costellated ; costellae, four to a 

 volution, granulated and equal. The anterior border of each volution has also a 

 depressed striated band; the volutions, about five in number, are flattened; the 



L2 



