﻿THE SINISTRAL GROUP. 



301 



Fig. 7 represents a specimen from the Cotteswolds in much better preservation 

 than the type (fig. 6) ; this has also rather a smaller spiral angle, and has probably 

 developed an additional whorl. 



Relations and Distribution. — " IAttorina" recteplanata seems generically related 

 to certain cylindro-conical forms of Amberleya which are rather characteristic of 

 the Lias. It is extremely rare. In the Inferior Oolite, besides the type, I know 

 of one specimen from Dundry and two from the Pea-grit of Longfords. Cf. also 

 " Monodonta" imbricata, Morr. and Lye, 'Grt. Ool. Moll.,' pt. 1, p. 67, pi. xi, fig. 3. 



237. Littorina {? Trochus) triarmata, Hebert and Deslong champs, 1860. Not 



figured. 



1860. Trochus triakmatus, Heb. and Desl. Foss. Montreuil-Bellay, p. 62 (sep. 



copy), pi. iii, fig. 5. 



A single specimen of this well-marked cylindro-conical form has come under 

 my observation ; it is somewhat longer and narrower than the type, but possesses 

 the characteristic ornamentation. 



It is apparently from North Dorset, and not improbably from the concavus- 

 zone of Bradford Abbas. In this case it may be an extreme " sport " of the poly- 

 morphous Littorina Dorseteusis. 



The Sinistral Group. 



This group comprises a number of shells which have been described under 

 Cirrus, Hamusina, 8cse,vola, and perhaps Tectus, the three last-named genera 

 having been constituted by Gemmellaro for the reception of species of this group 

 which occur in the Lias-Oolite of Sicily. Besides the common feature of being 

 sinistral, most of them are characterised by rugose ornamentation, by possessing a 

 shell more or less trochiform or turbinate, and in the case of Hamusina rather 

 thin. The aperture is circular, and there is scarcely any columella. Some 

 species, such as Cirrus nodosus, Sowerby, have an enormous umbilical excavation, 

 whilst in Hamusina the closure is complete. Nevertheless the presence or absence 

 of an umbilicus is probably not of much generic importance, though we may 

 make use of it for purposes of separating, for instance, Hamusina from Cirrus. 



This group, to judge from Gemmellaro's work, is evidently well represented in 

 the Lias-Oolite of Sicily. It is also fairly abundant in the lower division of the 



