TBTRANOTA CARRICKBNSTS. 41 



of the rock, but probably was obtained from the Drummuck Group (Up. Bala). 

 The Allt yr Anker specimen («/163*) recorded also by Salter in his 'Catalogue,' is 

 completely distinct from the Llanrwst shell and has been described on p. 33 of 

 this memoir as an undefined species of Bacania. 



As here stated, McCoy's definition of the species is made up from the com- 

 bined characters of the three specimens, and is consequently not applicable strictly 

 to any one ; the species, therefore, rests on an insecure foundation, though 

 probably the Mulloch Hill as well as the Llanrwst specimen is referable to the 

 genus Kolienospira. The Llanrwst specimen has a rather narrow, strongly-arched 

 dorsum, and the shell could not have been globose as McCoy describes it, the section 

 of the outer whorl being apparently parabolic; the slit-band is of moderate width, 

 well defined by raised edges, between which it is sunken ; the revolving lines 

 are sti'ong, equidistant, and few in number, four or five lying on each side of the 

 slit-band on the dorsum, and between these lines are very delicate revolving striae ; 

 the transverse strife are as strong or rather stronger than the revolving lines, are 

 nearly equidistant, and lie about the same distance apart as the latter, but are 

 rather less regularly placed, and curve back to meet the slit-band at about 45°. 



Gentis TETRANOTA, Ulricli and Scofield. 



Generic Characters. — Shell thin, involute ; whorls transverse, dorso-ventrally 

 compressed ; umbilicus open, large ; aperture moderately expanded, chiefly laterally, 

 transverse, wider than high ; inner lip without callosity ; dorsal sinus more or less 

 deep with a short central slit. Slit-band wide, elevated, bordered on each side 

 by a more or less raised edge ; about midway between it and the narrowly 

 rounded or angular umbilical edges there is a marked lateral ridge on each 

 side, occasionally dying out near aperture. Surface-ornamentation composed of 

 rather delicate sublamellose regular transverse lines of growth, often crossed at 

 right angles by another set of minute lines. 



No representative of this genus seems to have been previously described from 

 British strata. It was originally described from America by Ulrich and Scofield,^ 

 with Bacania bidorsata, Hall, from the Trenton Formation, as its type-species. 

 The error made by Koken in connecting generically several established European 

 Silurian and Devonian species with this American shell has been pointed out by 

 Ulrich and Scofield {op. cit.). 



1. Tetranota carrickensis, sp. nov. Plate VI TI, figs. 5 — 11. 



Specific Characters. — Shell subglobose, composed of 4 — 5 broad convex 

 whorls, scarcely overlapping. Umbilicus deep, exposing all the whorls, more 



I Ulrich and Scofield, op. cit., pp. 849, 875—877. 



