316 MALACOZOA. CEPHALOPODA. FOBAMINIFBRA. 



carinate margin ; the cells of the last turn about fifteen, 

 elevated narrow, convex, and with the concave interstices 

 transversely sulcate ; the centres elevated ; the end 

 moderately raised, semilunar, convex, with its sides em- 

 bracing the previous turn. Named after Miss Williamina 

 Macgillivray. 



Shell almost orbicular, the termination of the last turn rising 

 less than in the other species ; the sides equally convex, and 

 sloping from the centre to the margin, which is thin and sub- 

 carinate; the cellules in the form of rays, elevated, thin but 

 convex, glossy, smooth ; the interstices, in which are the dis- 

 sepiments, concave, transversely sulcate ; the end of the last 

 cell broadly semilunar, with a thick margin, which embraces 

 the preceding turn, and extends to the centres ; the aperture 

 small, roundish; the colour greyish-white. Diameter about 

 the sixtieth of an inch. 



Found by me, on the 7th January, 1843, on Pectinaria9 

 and Terebellee, on the beach near Aberdeen. 



3. Polystomella crenuldta. Crenulated Polystomella. 



Shell discoid, considerably compressed, with the sides 

 somewhat convex, the margin rounded ; the cells of the 

 last turn about twenty, prominent, curved, and regularly 

 transversely crenated, as are their concave interstices. 

 Crennldtus, with small crimples. 



Shell roundish, discoid, with the sides somewhat convex, 

 the margin rounded, the centres slightly depressed ; the rays 

 formed by the cells about twenty, curved, convex, and regu- 

 larly crenato-sulcate, as are their interstices, being marked 

 with concentric grooves and ridges ; the end of the last cell 

 semilunar, narrow, convex ; the colour pale bluish-grey. 

 Diameter about the fiftieth of an inch. 



This most beautiful species is much smaller than Polysto- 

 mella crispa, from which it differs in having the whole surface, 

 ridges as well as grooves, crenated, and the margin not thin, 

 but convex. In this last character it also differs from Poly- 

 stomella Gulielminse. 



Found by me, in December, 1 842, in shell sand, from Cruden 

 Bay, sent by Mr. Alexander Murray ; and in January, 1843, 

 adhering to Terebella conchilega, on the beach at Aberdeen. 



