1873.] MR. R. B. WATSON ON MADEIRAN MOLLUSKS. 38/ 



Rissoa sabulum, Cantraine. (Plate XXXVI. fig. 25.) 



Not in M'Andrew's list. 



Hab. Gorgulho, shore; Porto Santo, shore; Selvagens, shore; 

 Piedade (Cani<;al), 15-35 fathoms; Ponta de Sao Lourenco, 25-45 

 fathoms. 



There is great difficulty about the identification of this species. 

 Weinkauff (Conchylien des Mittelmeers) and Petit de la Saussaye 

 (Moll. d. Mers d'Europe) do not mention it. (Why?) Baron 

 Schwartz v. Mohrenstern holds the Madeira shells I sent him to be 

 Cantraine's species. Mr. Gwyn Jeffreys {in Hit.) rejects this 

 identificatioa For myself, if some shells procured from a dealer 

 really come, as they profess, from the Mediterranean, and are, as is 

 most probable, R. sabulum (by ovious error they were ticketed 

 R. glabrata), no doubt remains. Even to the microscopic markings 

 this Mediterranean species and my one from Madeira are identical. 

 But is this Mediterranean species the R. sabulum of Cantraine ? His 

 description is painfully vague, and is further in many points quite 

 inapplicable. The shell is not "subrimata" nor " corneo-cine- 

 rascente ;" the suture is not " submarginata ;" the mouth is not 

 "alba," nor is the lip "obtuso" nor " intus marginato." On the 

 whole, however, rather than risk falling into species-mongering, I 

 prefer to believe that his description was meant for this Mediterra- 

 nean species ; and in that case I have no doubt that my Madeiran 

 species is, as I have called it, the- R. sabulum of Cantraine. 



On the shore at the Gorgulho I found this species plentifully 

 living among the stony seaweeds which cover the rocks, and araon» 

 which Cardita calyculata, Saxicava rugosa, Rissoa pulcherrima, and 

 R. perminima, along with a Sipunculus {johnstonil) and other 

 creatures find refuge in great numbers. At Porto Santo the same 

 was the case. 



In my dredgings I only met with stray dead specimens. From 

 the Selvagens I found one or two specimens among other species 

 obtained on the shore, and which were given me by Baron do 

 Castello de Paiva. 



Mr. Jeffreys considers this the type of Von Muhlfeld's R. glabrata, 

 and says it is abundant throughout the Mediterranean. In that case 

 the identifications of Miihlfeldt's species by other writers are erro- 

 neous ; for the two species are certainly distinct. 



wf+i &\ Rissoa lincta, Watson. (Plate XXXVI. fig. 26.) 



Shell oblong, subcylindrical, obtuse, rather strong, glassily trans- 

 parent, and glossy, as if licked (lincta). 



Sculpture. Lines of growth rounded in outline, straight, very 

 slight, cross the whorls. 



Spiral striolaj can be seen with good light under the microscope, 

 excessively minute, flexuous, superficial, and impressed (not scratched). 

 It is their superficiality rather than their closeness which makes them 

 so difficult to see. They are not unlike (only much finer than) the 

 very minute striolse between the strise of R. striata. Three flatly 

 rounded spiral threads encompass the pillar, and appear faintly on 



25* 





