﻿RISSOINA. 



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206. Rissoina obtusa, Lycett, 1853. Plate XXI, figs. 10 a, 10b. 



1853. Rissoina obtusa, Lycett. Proc. Cottesw. Nat. Club, vol. i, p. 80. 



Bibliography 3 Sfc. — Lycett makes no mention of this species in the ' Cotteswold 

 Hills,' nor does Witchell enumerate any species of Rissoina in his ' Geology of 

 Stroud.' It is not absolutely certain that the species under consideration is the 

 one intended by Lycett, although his description tallies fairly. It must be 

 allowed, however, that the name " obtusa " is 'unfortunate, as this is rather a 

 slender shell. As a matter of fact an obtuse apex is characteristic of the genus, 

 although the earlier authors speak of Rissoina as pointed. 



Description : 



Length ..... 3*5 mm. 

 Spiral angle about .... 25°. 

 " Spire obtuse ; whorls slightly convex, six ; outer lip moderately large ; costaa 

 numerous, closely arranged, slightly curved from left to right." — Lycett, loc. cit. 



Relations and Distribution. — Found sparingly in the Pea-grit at Crickley and 

 Leckhampton. Rissoina Milleri, Lycett (Suppl., p. 18, pi. xliv, fig. 10), has some 

 resemblance. 



207. Rissoina gymnoides, sp. nov. Plate XXI, fig. 11. 



Description : 



Length . . . . .4 mm. 



Height of body-whorl to entire length . . 50 : 100. 



Spiral angle (obtuse) about . . . 22°. 



Shell subelongate, pupoid, scarcely turrited. Whorls about six, smooth, 

 convex, close; body-whorl about half the height of the entire shell. Aperture 

 square in front and slightly canaliculate, lips only moderately thickened. 



Relations and Distribution. — At first sight this might seem to be some form of 

 Pseudomelania, since the thickening of the peristome is less obvious than usual 

 in Rissoina. But the pupoid character of the spire militates against this supposi- 

 tion. It bears considerable resemblance to Rissoina gymna, Cossmann (fit. Bath., 

 p. 234, pi. xiv, figs. 23, 24), from which it differs in the greater relative length 

 of the spire and in having a wider spiral angle. Four specimens are in my 

 collection from the Lincolnshire Limestone of Weldon. 



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