352 MAZATLAH UNIVALVES 



4 4QI. MODULUS CATENULATUS, Phil. 



Trochus catenulatus, Kust. Syst. Conch. Cab. p. 110, no. 122, 



pi. 18, f. 4. Wee. in Zeit. f. Mai. 1850, p. 173, no. 33. 



C. B. Ad. Pan. Shells, no. 27% p. 190. 

 Modulus catenulatus, H. fy A. Ad. Gen. i. 317. 

 = Modulus trochiformis, Eyd. fy Soul. Voy. Bonite, pi. 36, 



f. 15, pi. 37, f. 2531 : B. M. Cat. p. 23, no. 177. 

 = Modulus Carchedonicus, P. P. C. Cat. Prov. : non A. Ad. 



loc. cit. : nee Monodonta carchedonius, Lam. An. s. Vert. 



vol. ix. p. 175, no. 7, ( = T. perlatus, Dillw. = T. unidens, Chem. 



teste Desk. : = T. unidens, D' Orb. B. M. Cat. Sagr. Col. p. 21, 



no. 233, pars.) 



The synonymy of this little understood genus has scarcely 

 been improved by Mr. Adams' monograph of the species in 

 the Cumingian Collection. The Lamarckian name is there 

 assigned to the M. Sayii, Nutt. ms., said to be from "Atooi, 

 California." The genus was not found by Nuttall in California, 

 and Atooi is in the Sandwich Islands. The Lamarckian 

 species, which may be the Caribbsean analogue of this shell, 

 T. angulatus, C. B. Ad., or a distinct species, must revert to 

 the old Chemnitzian name, M. unidens, teste Desk. 



The Mazatlan shell when adult has the general aspect of 

 a Trochus ; the spire being (more or less) elevated, and the 

 spire-outlines straight. The spire is covered with crowded 

 subgranulous revolving striae ; and the base, which is rarely 

 flattened, often much swollen near the very small umbilicus, 

 has about 8 rather deeply cut grooves. Colour varying from 

 white to light purplish brown ; generally with the latter in 

 dots. Labrum sharp, inside deeply grooved : periphery with 

 a very sharp keel, which in young shells, or after fracture, is 

 sometimes slightly waved, scarcely tuberculous. Operculum 

 multispiral (not paueispiral, as stated in Ad. Mon. loc. cit.) 

 with about 9 turns, very thin, transparent, edges irregularly 

 overlapping, rather concave outside, with the surface most 

 minutely granulose. The shells, though strong, had often 

 received severe fractures ; they were sometimes intrusted, and 

 occasionally incommoded by Ostrea conchaphila. Long. '77, 

 long. spir. '48, lat. "72, div. 70. 

 Hob. Mazatlan ; not uncommon ; Lpool fy Havre Coll. 



Tablet 1688 contains 4 sp. white. 1689, 3 do. flattened. 

 1690, 3 do. undulated. 1691, 4 sp. ordinary state. 1692, 3 do. 

 flattened. 1693, 3 do. deep colour. 1694, 3 do. undulated. 



