RADULA OF THE MITRID.E. 415 



one cusp, the 4th from inside, much the largest, next inside one 

 rather large, 11-12 in all, rapidly diminishing on both sides of 

 the big cusps, the exterior mere points. 



Another more mature specimen from Durban corresponds, 

 except that both the 4th and 5th lateral cusps are very large. 



Group (7) of sjyhcerulata. 



BJiachidian thick, deeply coloured with orange and brown, 

 bicuspid : laterals degraded, cusps few and obscure. 



1. 21. '■'■ circulata Kien. var." Durban (Mr. H. C. Burnup*). 

 Rhachidian thick, square, deep orange colour, opaque, with 2 

 prominent deeply-rooted cusps, the tips of which are blunt, and 

 do not project far beyond the upper margin, these ai"e flanked 

 on each side by two obscure denticles or wrinkles: laterals thin, 

 framework rather deep, with 4-5 deeply rooted denticles, 2-3 of 

 which incline inward, half the margin quite bare. There are 

 73 -f- nascent rows. 



Text-fifi-ure 13. 



Lateral and rliacliidiaii tooth of llitra sp7i(eritlafa Mart. 



There is evidently some confusion in the specimens forwarded 

 by Mr. Burnup, since those of " circulata " exhibit quite a diHerent 

 type of radula. Another specimen of " circulata var. " in my own 

 collection corresponds exactly with that here described. 



2. 21. crenifera Lam. Mauritius. Rhachidian squarish-oblong, 

 colour deep orange-brown, almost black, 6-cusped, the 2 central 

 strong, blunt and projecting, the side cusps smaller but distinct ; 

 base somewhat arched : laterals Avith 4-5 stumpy denticles, all 

 inclining inward, rest of margin blank. 



3. 21. sphceridata Mart. S. Pacific. Rhachidian lozenge- 

 shaped, with 2 large deeply rooted cusps mounted on a flat plate, 

 which is supei'posed on the main framewoi^k, tips broad, project- 

 ing well above the upper margin ; these are flanked on each side 

 by two small obscure cusps, set in the side of the tooth and some- 

 what behind ; sides of tooth sliglitly produced with small blunt 

 Avings ; base slightly arched : laterals consisting of an obscure, 

 rather deep-oblong plate, 3-cusped (some trace of a 4th) on inside 

 part of the inner margin, rest blank. Rows 634- nascent. 



In a specimen from Upolu (Coll. Cambridge) and in one from 

 Uvea (coll. A. H. C.) there are 4 lateral cusps. 



* Tliis form, hitherto confused with M. circida (not circulata) Kien., will be 

 described as M. biiniupiana. Mr. Burnup agrees that it is distinct. 



