RISSOA. 101 



liisMu iiiten-nptu, Johnston, Berwick. Club, vol. i. p. 271 (with animal). — Mac- 

 GiLLiv. Moll. Aberd. p. 150. — Buown, Illust. Conch. G. B. 

 p. 12, pi. 9, f. 45?— Menke, Zeitsch. Malak. 1845, p. 41. 



The Rissoa interrupta of authors being devoid of ribs 

 and in the more characteristic examples both thinner in 

 texture, and narrower and more elongated as well in gene- 

 ral shape as proportion of its several parts, has naturally 

 been reputed a distinct species. Nevertheless, as certain 

 individuals which present all its other peculiarities are 

 wholly or partially ribbed, some otherwise typical are solid, 

 and others again have the abbreviated shape and broad 

 volutions of pcirva proper, we cannot perceive any line of 

 demarcation between the two shells. The colouring ranges 

 fr6m the ordinary brown-zoned appearance oi parva, to 

 uniform horn-colour or dark rufous ; the two bands are 

 occasionally, also, broken up into squarish spots : occa- 

 sionally, likewise, the body is longitudinally painted with 

 slanting or wavy lines of rufous-brown, that are usually 

 but not invariably, interrupted in the middle, and emanate 

 below from the encircling basal band. In pre-eminently 

 aberrant individuals the spire exceeds the length of the 

 body, the basal declination of which is more rounded 

 than usual ; in such specimens the mouth is likewise nar- 

 rower than in ordinary. This smooth form, when adult, 

 has a labial varix similar to the ribbed variety. 



By the kindness of Mr. Jeffreys, we have figured (PI. 

 LXXXII. f. 8.) his unique example of B. Sarsii from 

 Loch Carron, which can only be distinguished from the 

 younger shells of the interrupta by its superior size and 

 ventricoseness. We do not know the Sarsii of Loven, but 

 his description agrees very fairly, except that the mouth is 

 stated to occupy but one-third only of the total length. 



We have delineated, likewise, (PL LXXXII. f. ].) a 



