MAZATLAN UNIVALVES 239 
scarcely develop the umbilical angle, the want of which in 
Prof. Adams’ description had led me to overlook the species. 
It somewhat resembles V. Panamensis, and is known from the 
other Mazatlan forms by the stout radiating bars, crossed by 
two central keels, on which the shell will stand without support. 
There is also an angle at the shoulder, and a fourth bounding 
the large umbilical region. The shoulder angle projects so as 
nearly to conceal the spire. Close to the suture is a swelling 
ridge, with a depression between it and the angle. This part 
is wrinkled, not always so as to correspond with the bars, which 
are variable both in number and prominence. The lip does not 
always end with a bar. The lip is waved as in Adeorbis, but 
the texture is semidiaphanous, porcellanous white, as in Vitrin- 
ella. The mean divergence, if the shoulder angle were rounded 
off, would be about 170°. ong. ‘02, lat. 05, by °087. 
Hab.—Panama: 13 sp. in sand; C. B. Adams—Mazatlan ; 
more than 30 sp. of Chamez and Spondyli; Z’pool Col. 
Tablet 1147 contains 5 sp. exhibiting the extremes of age 
and sculpture. 
297. ? VITRINELLA DECUSSATA, 2. Ss. 
2V.t. subelevatd, turbiniformi, tenui, alba, porcelland ; an- 
Sractibus iv. et dimidio, rotundatis, quarum ii. primi leves seu 
spiraliter striati sunt, subito in swperficiem decussatam mutan- 
tes; clathris extantibus quoad xv. spiralibus, transversis plus 
minusve distantibus, interstitiis valde impressis ; apertura, 
adolescente perttremati haud continuo, labio paullum in umbilico 
reflexo ; adulta circulart, continuo ; umbilico haud parvo. 
The true position of this shell cannot be determined till the 
animal and operculum have been examined. But for its tex- 
ture, which is that of Vitrinella, it might rank with Liotia. It 
is known at once by its Turbinoid shape, and by the beautiful 
decussation caused by prominent transverse and spiral bars. 
The large proportion of this shell which does not display the 
characteristic sculpture would favour the supposition of its 
being a young shell. About 30 specimens however (perfect 
and broken) were found, of which the greater part were of 
uniform size. The smallest specimen is *022 across. The 
largest measures long. ‘04, lat. ‘045 by °035, div. 115°. 
Hab.—Mazatlan ; very rare, off Spondylus; L’pool Col. 
Tablet 1148 contains 4 perfect and 2 imperfect specimens, 
shewing variations in age and sculpture. 
