CYRTOLITES. 23 



angulated and sides gently convex. Umbilicus open, shallow, exposing all inner 

 whorls. Whorls crossed by regular strong equidistant thin transverse prominent 

 lamellas, in places minutely fimbriated, and having several very fine transverse striae 

 in interspaces; lamellas more crowded and slightly sigmoidal near mouth, being 

 arched gently back on sides of Avhorls and then forwards, but apparently sharply 

 bent back close to dorsal keel so as to meet it at about 45°. Slit-band absent ? 



Dimensions. — Height about 30 mm. 



Horizons. — (1) Upper Arenig; (2) Llandeilo Flags. 



Localities. — (1) Llanvirn Quarry; (2) Abereiddy Bay ; Traethllwyn, Llanrhian, 

 St. Davids. 



Remarks. — Hicks's definition of this species was as follows : " Spire of three 

 very rapidly increasing whorls. Outer whorl greatly expanded, but compressed. 

 Lines of growth strongly marked, arched backwards and approximating to each 

 other more closely in the expanded outer portion. Diameter 1^ inch." Neither 

 the type [28001] in the Jermyn Street Museum nor the counterpart of the type 

 in the Sedgwick Museum are well preserved, both being flattened and somewhat 

 distorted, but in the latter we seem to be able to detect a sharp bending of the 

 transverse lines close to the dorsal edge, and also the presence of intermediate strige. 



The specimens [28018, 28019, 28020] from the Llandeilo beds of Abereiddy 

 Bay in the Jermyn Street Museum are better preserved than the type, but were 

 labelled B. pcrtnrhatus {_= Fj. fennistriatns'\, from which they differ considerably 

 in ornamentation. 



The generic reference of this species is a matter of uncertainty, the rapid 

 enlargement of the outer whorl and the ornamentation being unlike that of 

 Oxijdiscus, and if a slit-band is present it may be referred to Oonradella . 



Genus CYRTOLITES, Conrad. 



Generic Characters. — Shell composed of few whorls (2 — 3), not overlapping, 

 scarcely contiguous, the last occasionally free, enlarging rapidly to mouth; dorsum 

 carinated ; whorls occasionally with weak lateral carina on each side giving a 

 broadly lanceolate or snbquadrate section; no apertural sinus; mouth simple, 

 entire; sides of whorls usually with transverse swellings or ribs more or less 

 developed, or transverse lines meeting the keel at a large angle. 



The type of this genus is Gi/rfolites ornatns, Conrad,^ and Koken's ^ definition 

 of the genus in 1896 agrees with this form, whereas Ulrich and Scofield's ^ is 

 too wide and includes species probably referable to Koken's Temnodiscus (1897 

 nan 1896). Perner * has remarked that the genus Gyrtolites contains a rather 

 heterogeneous assemblage of species, and the Bohemian forms do not appear to 



1 Conrad, * Ann. Eept. Nat. Hist. Surv., New York,' 1838, p. 118. 



8 Koken, ' Die Leitfossilien ' (1896), p. 100. ^ Ulrich and Scofleld, o]j. ciL, pp. 846, 858. 



* Perner, op. cit., p. 79. 



