ang MAZATLAN UNIVALVES 
401. MoptLus catenunatus, Phil. 
Trochus catenulatus, Kust. Syst. Conch. Cab. p. 110, no. 122, 
pl. 18, f. 4—Mke. in Zeit. f. Mal. 1850, p. 173, no. 338.— 
C. B. Ad. Pan. Shells, no. 273, p. 190. . 
Modulus catenulatus, H. & A. Ad. Gen. i. 317. 
= Modulus trochiformis, Hyd. & Soul. Voy. Bonite, pl. 36, 
f. 1—5, pl. 37, f. 25—31:—B. M. Cat. p. 23, no. 177. 
= Modulus Carchedonicus, P. P. C. Cat. Prov.:—non A. Ad. 
loe. cit.: nee Monodonta carchedonius, Lam. An. s. Vert. 
vol. ix. p. 175, no. 7, (=T. perlatus, Dillw.=T. unidens, Chem. 
teste Desh. :=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 Caribbean analogue of this shell, 
T. angulatus, C. B. Ad., or a distinct species, must revert to 
the old Chemnitzian name, M. unidens, teste Desh. 
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 striz; 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 paucispiral, as stated in Ad. Mon. loc. cit.) 
with about 9 turns, very thin, trangparent, edges irregularly 
overlapping, rather concave outside, with the surface most 
minutely granulose. The shells, though strong, had often 
received severe fractures ; they were sometimes incrusted, and 
occasionally incommoded by Ostrea conchaphila. Long. ‘77, 
long. spir. 48, lat. °72, div. 70°. 
Hab.—Mazatlan ; not uncommon; L’pool & 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.— 
