2 CHASTER : NEW MARINE MOLLUSCA FROM TANGIER. 



Amongst other noteworth}' fcrms are Rissoa farvula, R. 

 fischcri and R. tnrricula of Jeffer}S, Marginella gnancha, d'Orb. 

 Rissoa (Alcidia) spinosa, Monts., as well as the forms described 

 below. 



Coecum cuspidatum (Monts., MSS.), sp. nov., PI. I, Fig. 4. 



Shell comparatively long and slender, slightly curved, 

 glossy, pellucid, sculptured with numerous but obscure lines of 

 growth ; the diameter increases very slightly and gradually 

 towards the mouth ; septum much produced in the form of a 

 cone with slightly concave sides, ending in a fine point, and not 

 deviating to either side ; mouth not thickened by an annular 

 rib. Length, 2-5 mm. 



Several specimens of this species were found both in the 

 dredgings and shore drift. One other species (undetermined) of 

 the genus was met with. 



Retrotortina, gen. nov. 



Shell minute, coiled in a left-handed direction, spire 

 depressed, mouth nearly circular, umbilicus large. The species 

 for which I suggest tiiis genus is interesting, representing as it 

 does the sinistral (or probably far more correctly, pseudo-sinistral) 

 form of a series of which Skenea and Hcmalogyra are respectively 

 the dextral and planospiral members. 1 he progressive 

 diminution in size is also noteworth}-, for Retrotortina is even 

 more minute than Homalogyra. 



Retrotortina fuscata, 5/. nov., PI. I, Figs. 5 and 6. 



Shell minute, left handed, brown in colour, glossy, marked 

 with numerous lines of growth ; whorls, two, convex ; suture, 

 deep ; spire nearly flat ; mouth almost circular, somewhat 

 oblique ; umbilicus very large. Diameter, -5 mm. 



A few specimens from shore drift. Unfortunately no live 

 examples occurred, consequently until the operculum can be 

 examined it must remain a matter of some slight uncertainty 

 whether the shell is pseudo-sinistral or sinistral. The other 

 members of the family found were Skenea planorbis, Fabr. and its 

 var. inaculata, Jeff., 5. pelhicida, Monts., and two species of 

 Homalogyra. 



