330 MISS DONALD ON PROTEROZOIC GasTEROPoDA [May 1902, 
form, combined with the angular whorls, distinguishes it from all 
other species. 
Dimensions.—There are five whorls, with the impression of 
three more in the matrix. The length = 23 millimetres, and the 
width = 8 millimetres. 
Locality and Horizon.—Shalloch Mill (Ayrshire), in rocks 
of Middle Bala age [ Lapworth ]. 
Genus Turritoma, Ulrich.? 
Diagnosis.—Shell elongated, consisting of numerous whorls. 
Whorls somewhat flattened, convex above, slightly concave in the 
middle, and most prominent in the lower part where the band is 
situated ; other features apparently as in Hormotoma. 
Type, 7. acrea (Billings). 
Ulrich states that 
‘this is a well-marked group of species, readily distinguished from Hormotoma 
(to which the group is related) by the flattened instead of uniformly rounded 
volutions, and by the lower position of the band.’ 
Besides the type, he considers that it includes 7’. Ada (Billings), 
T. Boylei (Nicholson), 7’. constricta (Whiteaves), 7. cava (Lindstrom), 
and 7. Laphani (Hall). The tyne, judging from the figure, 
apparently has the whorls slightly convexo-concave, but this does 
not appear to be the case with Murchisonia Boylet and M. Laphami ; 
indeed, Nicholson states that the whorls of the former are flat.? 
Remarks.—In Mrs. Gray’s collection I have met with two species 
which correspond more nearly to the diagnosis of Turritoma than 
that of any other genus, except that the whorls are not convexo- 
concave, but flat or very slightly convex. I therefore refer them 
here provisionally. They differ from Hormotoma in this flatness of 
the whorls, in the less produced base, and also in the band being lower 
than is usually the case in that genus. The form of the band and 
the direction of the lines of growth are similar to those of Hormotoma. 
They have most in common with H. cingulata (His.),’ the flattened 
whorls and low-lying band of which caused me to regard it.as a 
doubtful member of the genus; and if the convexo-concavity of the 
whorls be not an essential character of Turritoma, that species should 
perhaps be removed hither. 
TuRgitoma (?) Porta, sp. nov. (Pl. VIII, figs. 7 & 8.) 
Diagnosis.—Shell conical, of moderate size. Whorls about ten, 
somewhat flattened, and but slightly convex, smooth. Sinual band 
near the middle of the body-whorl, but very low down on the 
earlier whorls, appearing just above the suture, broad, flat, level 
with the surface, limited on each side either by a groove or by a 
slight, raised thread. Lines of growth curving obliquely back to 
the band above, much more obliquely forward below, and curved 
! Final Rep. Geol. & Nat. Hist. Surv. Minnesota, vol. iii, pt. ii es! p. 959. 
> Quart. Journ. Geol. Soc. vol. xxxi (1875) p. 547. 
hid, vol. ly (1899) p, 263. 2 
