PHRAGMOSTOMA DECIPIENS. 85 



umbilical slope very steep. Whorls transverse, low, about twice. as wide as high, 

 with distal third of outer whorl nearly straight, increasing slowly in height to 

 mouth but more rapidly in height in distal third; dorsum gently rounded or 

 slightly flattened except in distal third where it becomes carinated with a sharp 

 median angulation. Mouth transverse, slightly expanded at sides (but not 

 abruptly), with lower lip reflected and thickened ; upper lip not reflected or 

 thickened, but with broad open very shallow V-shaped emargination followed by 

 long narrow median slit and then by slightly depressed band showing obscure 

 traces of small oval foramina. Surface of shell ornamented with (1) closely-placed 

 fine transverse striae, becoming stronger and squamose near margins of aperture 

 and curving back to meet median line at about 00°; and with (2) weak low rounded 

 regular equal revolving ridges parallel to median line and becoming stronger and 

 more distinct on umbilical slopes where they are slightly oblique to the suture-lines, 

 and are finely cancellated by the transverse stria*. 



Dimensions. — Height, c. <><> mm. ; thickness, c. 20 mm. ; diameter of umbilicus, 

 c. 24 mm. 



Horizon. — Mulloch Hill Group, Llandovery Series. 



Locality. — Mulloch Hill, Girvan. 



Remarks. — This large shell, of which the types are in Mrs. Gray's Collection, 

 was referred by McCoy to Tr. dilatatus (Sow.), and in fact he only mentioned this 

 Girvan locality for the occurrence of the species. The specimens which he thus 

 labelled in the Sedgwick Museum and the more abundant and more illustrative 

 material in Mrs. Gray's Collection show that it cannot be considered identical with 

 Sowerby's form. The non-reflection of the upper lip of the mouth, the narrow 

 median dorsal slit, the much smaller expansion of the mouth and depressed median 

 band are sufficient to separate it, though the general shape of the shell and 

 character of the ornamentation are on the whole closely similar. Indeed there was 

 at first some doubt in my mind whether it was separable from the form from 

 Woodland Point described above as Trent, dilatatus var. girvanensis, but the 

 reduced sharpness of the umbilical edge, the presence of the median slit on the 

 dorsum, the simple non-reflected and un thickened upper lip, the straightening of 

 the last part of the outer whorl, the strong transverse striae and the depressed 

 median band are distinguishing features. The ornament of longitudinal revolving- 

 lines is almost identical. As to the genus to which this Mulloch Hill shell should 

 be referred, Phragmostoma seems more suited to receive it than Trematonotus, and 

 we may compare Phr. ciuis (Barr.) 1 from Stage Ee 2 for the double ridge or 

 slit-band on the last whorl and for the ornament, and Phr. nobile (Barr.) 2 for the 

 carination and foramina near the mouth. 



1 Peruer, op. cit., p. 125, pi. cciv, figs. 20— 30 ; text-figs. 89, 90. 



2 Ibid., p. 122, pi. lxxxii, figs. 6, 7 ; pi. lxxxvi, figs. 43, 44 ; text-figs. 87 a — d. 



