1881.] SHELLS FROM SOCOTRA. 253 



5, well rounded. Aperture obliquely and broadly ovate, angular 

 above, suboblique. Peristome thick and solid, particularly on the 

 columellar margin, where it spreads out and completely conceals the 

 umbilicus ; this is a greater development and exaggeration of the 

 angulate notch which is to be seen in the next two species from 

 this island. Operculum situated well within the aperture, flatly 

 concave in front, shelly, smooth, of about 3| whorls, nucleus sub- 

 central. 



Size of largest specimen — major diara. 59'5, minor diam. 5*1, alt. 

 axis 315 millims. Largest size given by Pfeiffer — major diam. 4 TO, 

 minor diam. 34*0, aperture 19x16 millims. 



Example figured — 



major diam. 2'15. minor diam. 1*7, alt. axis 1 '35 inch. 



,, „ 54, „ „ 42-5, „ 34-0 millims. 

 Small var. — 



major diam. 38, ,, „ 30"7, „ 18*5 „ 



„ „ 1*32, „ „ 1*0, „ 0*53 inch. 



Animal not yet examined. 



[" Very common on the limestone plains from more than one 

 locality."" (I. B. B.)] 



0. guillani, Petit, is a small form, diameter 26 millims., very 

 similar in the expansion of the columella-notch over the umbilicus, 

 from Mogadoxa on the N.E. coast of Africa, 250 leagues distant 

 from Socotra. 



Otopoma balfouri, n. sp. (Plate XXVII. figs. 2, 2 a.) 



Shell globosely turbinate, solid, verj' openly umbilicated, ribbed 

 regularly and spirally throughout ; but the ribbing does not extend 

 within the umbilicus ; colour white ; spire pyramidal, decollate 

 usually for 1^ whorl; suture well impressed; whorls 4, well 

 rounded ; aperture subvertical, ovoid, angular above ; peristome 

 continuous, solid, and reflected slightly on the outer margin, less 

 solid on the columellar side, which presents a slight dentation with 

 angularity just below the upper inner margin, well rounded below. 



Size :— 



Major diam. 55*0, minor diam. 400, alt. axis. 22-0 millims. 

 ,, „ 2-16, ,, „ r58, „ 0-87 inches. 



Dwarf var. 



major diam. 32-8, „ „ 26"5, „ 14 millims. 



[" Common on the land towards the east end of the island : this por- 

 tion is elevated over 700 feet and is of limestone." (I. B. B.)] 



This species is very close to 0. auriculare, Gray, of which the 

 habitat is unknown, but the columellar margin is more expanded 

 and the ribbing is coarser and more distant than in O. balfouri. 



Cyclostoma albicans, Sow , apud Gray, Zool. Beechey's Voy. 

 pi. xsxviii. fig. 30, p. 146, is said to inhabit some of the islands of 

 the Southern Pacific, which I do not believe is correct. The descrip- 

 tion agrees with this shell ; but no dimensions are given, and the 



