i65 

 ADDITIONS TO "BRITISH CONCHOLOGY." 



(Continued from page 138). 



By. J. T. MARSHALL. 



Homalogyra atomus Phil, {continued). 

 Var. polyzona Brus. {Irish Nat., vol. 6, p. 125). — Rathlin 

 Island, Antrim (Chaster). This differs from the type in having a 

 sculptured periphery. 



Although usually living in Chrondus crispus and other dwarf sea- 

 weeds, in one locality at Guernsey this species occurs plentifully under 

 smooth stones with Rissoa cingillus. 



H. rota F. & H.— Scilly Isles (Burkill andJ.T.M.); Port Erin 

 (Leicester) ! Antrim (Chaster); Cumbrae (Robertson); Ayr Bay and 

 Campbelltown Loch (Scott)! W. Sutherlandshire (Baillie and J.T.M.); 

 Jersey, Guernsey, and Herm ; Torbay; Killala Bay; Connemara; 

 Eigg Island; Oban. Raised beach at Shewalton, Ayrshire (Scott) ! 



Even this minute shell has its dwarf form, specimens from Iona 

 being only a quarter the size of those from Guernsey, where the 

 largest occur. 



Caecum trachea Mont. — Lamlash Bay, Iona, Sound of Sleat, 

 and Loch Inver (Somerville and J.T.M.) ; Guernsey, rare; Scilly 

 Isles ; Skegness ; Connemara ; Mayo ; Sligo ; Iona ; the Minch off 

 Loch Boisdale, 35 f., a young specimen, the furthest northern point 

 recorded. 



The concentric rings which characterise this species are of every 

 degree of coarseness, and the she41 also varies in the degree of curva- 

 ture. Young shells are more curved and tapering, not more "convex" 

 as misprinted in " British Conchology." 



C. glabrum Mont. — From very fine sand dredged off Guernsey 

 remarkably long and curved specimens occur, some being equal in 

 length to two ordinary examples, and forming almost a half-circle. In 

 this stage it is the Brochus arcuatus of Brown, who also made two 

 other species of different stages of the young. The shell of the fry is 

 at first a little fiattish coil of 2-3 whorls, and then gradually lengthens 

 out as shown in Jeffreys' figure. The young must be searched for 

 with a microscope, and care must be taken not to confound them with 

 the fry of Cydostrema serpuloides with which they live, for they are 

 remarkably alike ; but the latter, though of microscopic size, are 

 shaped like the parent, or a minute Helix ericetorum, whereas the baby 

 Cceca are shaped like a miniature Valvata cristata. The drift sand 

 from Dogs' Bay, Connemara, is peculiarly productive of this embry- 

 onic shell, but here again the fry of Cydostrema serpuloides is equally 

 abundant. 



