THE BRITISH NATURALIST. 



123 



in size and arranged regularly to which the varietal name has been 

 given of ecannata, Monts. This var. is most frequently found 

 with varices and probably the var. varicosa Mar. of Mr. Somerville's 

 marine list is a synonym, though I am not aware of any description 

 of it beyond the mere name. This is undoubtedly a rare shell with 

 us, though it seems to be of universal occurrence in the Mediterranean, 

 but I fancy that in its known localities it only wants looking for to be 

 turned up in some numbers alive. My experience of it is confined 

 to the Channel Isles, and its habitat is most usually under stones 

 which are rather deeply buried in the sand, to which it moors itself by a 

 strong byssus. There is quite a special population in this kind pf 

 habitat, and it may surprise some collectors to know that it is any use 

 turning up the stones which are firmly embedded in the ground, and 

 apparently offer no facilities of ingress or domicile to Mollusca. And 

 yet here is the native haunt of a small number of very interesting species. 

 Under stones which are so buried about half way up the shore occur 

 Alexia bidentata, Rissoa cingillus and R. striata very commonly, while at 

 extreme low-water one gets in Guernsey and Herm at any rate 

 Adcorbis, Chiton scabvidus, Rissoa striatula, and Lima Mans . var. tenera ; 

 in Jersey Rissoa lactea also is not scarce, though called by Jeffreys our 

 rarest Rissoa. I have seen 14 stviatulas on a single stone but this was 

 an exceptional haul. As for Chiton scabvidus — a species which seems 

 very little known to collectors — it is abundant in this habitat and 

 assiduous collecting for a couple of weeks is sure to produce 50 or 60. 



Rissoa lactea, Mich., the next species on our list, can be soon 

 dismissed. It is like the preceding species in being quite removed 

 from any other species in the genus, and consequently is relegated by 

 the authors of the " Moll. Marins du Rpusillon " I. 298 to a new sub- 

 genus Massotia. It bears, however, a sufficiently close resemblance to 

 the contour and sculpture of the Alvanias to be merged with them. 

 The characteristics are a remarkably oval form, with a last whorl 

 taking up three-quarters of the shell and a spire almost sunk. The 

 sculpture is a slight and fine lattice-work and distinguishes it at 

 once from the other species {cancellata, etc.), which have a dispropor- 

 tionately large last whorl. The species on the other hand which have 

 fine sculpture (e.g. punctura, reticulata) will be known from lactea by a 

 pronounced pointed spire. Colour very much as in striatula : size 

 5 — 6 mm. 



Varieties : var. major, Requien. 



var. minor, Requien. 

 I am not aware of the requisite proportions of these rather un- 

 necessary vars., as they are not given in any book to which I have 

 access. The habitat of this shell has been above referred to. 

 Llandaff. 



