MAZATLAN UNIVALVES 4A) 
found vary in proportion: the smaller, with 6 normal turns, 
measuring long. ‘06, lat. °028. 
The larger er US7, a7) ates 
Hab.—Mazatlan ; extremely rare, off Spondylus ; L’pool Col. 
Tablet 2026 contains the larger specimen. 
* 
556. LEIOSTRACA PDISTORTA, var. YOD. 
Melania distorta, Phil. Moll. Sic. vol. i. p. 158, pl. 9, f. 10. 
Kulima distorta, Desh. in Lam. An. s. Vert. vol. viii. p. 454.— 
Phil. loc. cit. vol. i. p. 135.—Forbes & Hanl. Brit. Moll. 
vol. iu. p. 232.— Clark, Moll. Test. Mar. Brit. p. 451. 
Leiostraca distorta, H. & A. Ad. Gen. i. 236. 
Lt. “DL. distortea” simillind, sed minima; parte suturali 
paululum latiore. 
The type of Leiostraca iota, OC. B. Ad. erroneously labelled 
‘Jamaica’ in Mus. Cuming, and very incorrectly figured by 
Sow. is somewhat broader and less bent than the Mazatlan 
shells: in other respects it exactly accords. After repeated 
comparison of very fresh specimens with the British dwarf 
variety of L. distorta, the characters appear exactly alike, 
except that the sutural portion, which (the shell being tran- 
sparent) gives an appearance of a spiral line, is slightly nar- 
rower in the Scarborough specimens received from Mr. Bean. 
The same glégsy deposit over the base, with the rather separate 
parietal lip, giving in some directions of light the appearance 
of an umbilicus, appears in each, and of the same shape. No 
differenee can be traced in the minute vertex, nor in the varices. 
The colour in fresh specimens exactly accords. The specimens 
in Mr. M’Andrew’s collection, grouped under Eu. distorta, vary 
extremely in size and arcuation. The Mazatlan shells are on 
a much smaller scale, generally more bent, and most beautifully 
glossy and transparent. The same form occurs in the West 
Indies (B. M.). According to Deshayes (Lam. An. s. Vert. 
vol. vil. p. 455, no. 8) it is found fossil in Grignon and other 
places. Ifit extends so far back in time, it is natural that the 
living shell should occupy a widely distributed space. As 
however the animals may be distinct, both in this and in L. iota, 
a name is added expressive of its (for the genus) extreme 
minuteness. The smallest sp. (of 3 normal whirls) measures 
‘035 by ‘016. A remarkably large sp. measures long. *082, 
long. spir. °055, lat. °033, div. 18°. 
