230 MAZATLAN 'UNIVALVES 



? = Troclius (Calcar) stellaris, Mice, (non Lam.) in Zeit.f. Hal. 

 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 

 description) 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, pi. 5.=Pomaulax u. Gray*) is a 

 very large Californian species, the singular triradiate opercu- 

 lum of which was found fresh in, the S. 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 rugulse 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 (6 8 appearing) crossed by very 

 close sharply-raised lines of growth, and faintly denticulating 

 the base of the labrum. Periphery with a variable number 

 (1418, generally 16) of rounded palmse, 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 Algse, Corallines, Annelids, Bryozoa, Vermetidse, &c. ; and 

 also, not unfrequently, attacked by Gastrochsena 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. balsenarum, Val. 

 Toy. Ven. and differs in the style and number of nodosities in the whirls. In T. 

 balenar\im 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 much larger than in T. balsenarum." Baird. T. balse- 

 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. 



