230 MAZATLAN UNIVALVES 
?=Trochus (Calcar) stellaris, Mie. (non Lam.) in Zeit. f. Mal. 
1850, p. 172, no. 30. 
This most abundant Mazatlan shell not being quoted by 
Menke in his catalogue, while the true T. stellaris (Stella st. 
Gray) is a well known E. Indian shell, it is natural to suppose 
that his T. stellaris (which is published without a word of 
deseription) either belongs to this species, or has been im- 
ported.— The Cumingian specimens had (by an oversight) 
been marked T. undosus. The true T. undosus, Mawe, (Wood 
Ind. Test. Suppl. p. 16, no. 1, pl. 5.=Pomaulax u. Gray*) is a 
very large Californian species, the singular triradiate opercu- 
lum of which was found fresh in the 8. W. Mexican collection. 
Shell yellowish white, somewhat silvery at the mouth; more 
or less conical, with irregular, radiating, somewhat diagonal 
rounded plications, and often finely tubercular rugule between; 
slightly swollen next to the suture, and slightly concave above 
the periphery, but flattened in its general aspect. Base with 
rounded close spiral ridges (6B—8 appearing) crossed by very 
close sharply-raised lines of growth, and faintly denticulating 
the base of the labrum. Periphery with a variable number 
(14—18, generally 16) of rounded palme, more or less projecting, 
more or less broad, concentrically furrowed by the basal ridges 
of growth, and not necessarily connected with the external pli- 
cations. Aperture with the labrum developed along half a whirl, 
uniting with the parietal labium which covers half the base, 
expanding over the umbilical region and ending in a raised 
portion below the axis. Columella with two spiral umbilical 
grooves, of waxen aspect, separated by a white rounded ridge 
ending in a tubercle just outside the mouth. The labrum is 
indented by the exterior plications which are at right angles 
to its margin. The shell is rarely seen in perfection, being 
almost always covered, even when young, with a variety 
of Alge, Corallines, Annelids, Bryozoa, Vermetide, &c.; and 
also, not unfrequently, attacked by Gastrochena truncata and 
Lithophagus aristatus. Even the base; to the very edge of the 
labium, is frequently covered. The operculum differs from 
*<«<T. undosus, Wood, is a very much smaller shell than T. balenarum, Val. 
Voy. Ven. and differs in the style and number of nodosities in the whirls. In T. 
balenarum these amount in the last whirl to five rows, all much of the same size 
and round form. In T. undosus there are only two rows, and the upper of these 
are long, not round, and uch larger than in T. balenarum.” Baird.—T. bale- 
narum is generally regarded as a variety of T. undosus, in which the upper long 
row of tubercles is broken up into smaller rounded ones. If the two forms are 
however constant in their respective provinces, they may be representative species. 
