MAZATLAN UNIVALVES 343 



no. 374, p. i?,. — Eijd. Sf Soul. Voy. Bon. pi. 39, f. 6, 7 :— 



B. M. Gat. p. 34, no. 188. 

 Cerithidea Montagnei, Mwi. loc. cit. p. 83. 

 = Cerithinm Eeevianum, C. B. Ad. Pan. Shells, no. 205, 



pp. 156, 310. 

 Comp. Ceritkiimi pulclirum, C. B. Ad. loc. cit. no. 204. 



That the Mazatlan sheU is identical mth C. Eeevianum. and 

 with D'Orb.'s species, is evident from a comparison of types. 

 It is possible that Sow. is right in uniting also the C. pulchrum. 

 But in affiliating the China species C. Fortunei, A. Ad. (Mon. 

 1. c. no. 20) and C. LargiUierti, Phil. (Zeit. f. Mai. 1848, p. 20, 

 no. 83,) the latter as the young of the S. American, he displays 

 a judgment only surpassed in singularity by that of Dr. Gray, 

 who calls this species "only a variety of C. varicosum without 

 varices," (B. M. Cat. loc. cit.) Kiener's figure is not charac- 

 teristic ; nor was U Orb's sufficiently accurate for Prof. Adams 

 to recognize the species. 



None of the Mazatlan shells are so broad va. proportion as 

 C. pulchrum, C. B. Ad., nor possess its sculpture. This is stated 

 to have 4D ribs on each whirl ; Mr. Cuming's type however has, 

 as the spire ascends, about 4D, 31 and 26 respectively. It differs 

 hi its regular varices, 240" distant, and in the spiral stria;, one 

 of which is conspicuous to the top of the non-decoUated spire. 

 The continuity of the labrum and labium, by which it is 

 further distinguished, depends on age, and is equaled in the 

 typical form. If a variety, it is a constant one, as Prof. Adams 

 found 125 specimens, living with the other species. 



The Mazatlan specimens of C. Montagnei vary considerably 

 in the elongation and divergence of the spire, in the number 

 and strength of the ribs, and in the amount of spiral sculpture. 

 In the upper whirls the ribs are comparatively distant, sharp, 

 and never tuberculous. On the last whirl they are often very 

 close (sometimes with a sudden change,) sometimes nearly 

 obsolete, sometimes spirally subnodidou^ ; varying from 26 to 

 about 48. There is always a raised line continuing the suture, 

 (very rarely visible in the suture of elongated specimens,) and 

 numerous spiral stria) round the base. The surface under the 

 microscope is often most minutely corrugated ; and the epider- 

 mis, which is thin and deciduous, is spirally striated, or striato- 

 corrugated. No varices are ever seen on the spire ;^and it is 

 only a very rare accident if one other is seen besides the 

 terminal one. The labrum is widely reflected, often in layers ; 

 and in the adult there is always a considerable thickening of 



