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Show 1873.] MR. R. B. WATSON ON MADEIRAN MOLLUSKS. 387 RISSOA SABULUM, Cantraine. (Plate XXXVI. fig. 25.) Not in M'Andrew's list. Hab. Gorgulho, shore; Porto Santo, shore; Selvagens, shore; Piedade (Canigal), 15-35 fathoms; Ponta de Sao Lourengo, 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 litti) rejects this identification. 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 1 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 Mediterranean species ; and in that case I have no doubt that m y 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 among which Cardita calyculata, Saxicava rugosa, Rissoa pulcherrima, and R. perminima, along with a Sipunculus (johnstoni 1) and other creatures find refuge in great numbers. At Porto Santo the same was the case. In m y 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 Miihlfeld's R. glabrata, and says it is abundant throughout the Mediterranean. In that case the identifications of Miihlfeldt's species by other writers are erroneous ; for the two species are certainly distinct. RISSOA LINCTA, Watson. (Plate XXXVI. fig. 26.) Shell oblong, subcylindrical, obtuse, rather strong, glassily transparent, and glossy, as if licked (lincta). Sculpture. Lines of growth rounded in outline, straight, very slight, cross the whorls. Spiral striolae 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 striolae between the striae of R. striata. Three flatly rounded spiral threads encompass the pillar, and appear faintly on 25* |
