476 MAZATLAN UNIVALVES 



But in some few specimens the labial callosity is no larger 

 than in some of P. patula, jun. : the labral teeth are scarcely 

 developed : the mouth is more open, and the sculpture less 

 decided. It then so closely resembles young specimens of 

 P. patula that they can only be separated by a balance of 

 characters. The opercula examined scarcely differ from 

 those of P. patula except in their lighter colour. There 

 were however none of P. patula, jun. of the same size to 

 compare with them. The largest normal specimen mea- 

 sures long. 1*58, long. spir. '5, lat. 1'14, div. 90. 

 An elevated sp. 1'42, '52, '93, 70. 

 The largest, abnorm.,, 2 '12, '67, 1'5, 90. 

 The smaUest adult '97, '46, '58, 70. 



Hob. Galapagos, Cuming. Mazatlan ; not uncommon, often 

 rubbed, but rarely encrusted ; L'pool Col. 



Tablet 2221 contains 4 sp. normal. 2222, 1 do. with opercu- 

 lum. 2223, 4 sp. elevated spire. 2224, 5 sp. aperture con- 

 tracted. 2225, 7 do. aperture deformed. 2226, 2 sp. sculpture 

 well developed. 2227, 4 sp. columellar fold evanescent. 2228, 

 3 do. closely approaching P. patula. 2229, 3 opercula, of 

 which one is abnormal, with subcentral nucleus. 



Monoceros muricatum, Itve. Condi. Ic. pi. 2, sp. 7. 

 Monoceros muricatus, Mke. in Zeit.f. Mai. 1850, p. 179, no. 45. 

 = Purpura cassidiformis (Blainb.) D'Orb. B. M. Cat. Moll. 



p. 41, no. 361. 

 =Purpura truncata, Duel, teste Mice. 



This shell rests its claim to a place in the genus Monoceros 

 on a projecting wave in the labrum between the canal and the 

 first costal depression. Of the true Acanthine Purpuridse, 

 the almost peculiar possession of the West Cpast of America, 

 not a single specimen occurred. The few Mazatlan specimens 

 of this shell are strongly foliated over the principal spiral ribs, 

 and almost always encrusted. The operculum is not so small 

 in proportion as in P. patula, with the margins well rounded, 

 and of a reddish chocolate colour. "Deckel hornig, biegsam, 

 durchscheinend," Mke. Long. 2' 52, Iwng. spir.'SA, lat. 2' 2, 

 div. 11. 





