298 PROCEEDINGS OF THE NATIONAL MUSEUM. voi..xxiv. 
EXPLANATION OF PLATES. 
The figures are all largely magnified. The length of the aetual specimen!?, Nos. 1 
and 2, are respectively twenty and sixteen hundredths of an inch; the diameters of 
the same, nine and six hundredths of an inch. The robust example, 18, is 0.23 by 
a diameter of a trifle over 0.1 of an inch. These dimensions exceed the average of 
any large number of shells. Particular attention is called to the variation in size 
and form of the aperture. The figures were all drawn V)y Dr. J. C. McConnell, 
whose skill and taste are too well known to require praise. 
Plate NLX. 
Piiliidcslrina protca Oould. 
Slender, elongated forms with rounded whorls. 
Fig. 1. Whorls smooth, without sculpture. 
2. Same as above, dwarfed form. 
3. Whorls spirally threaded or lirate. 
4. Shorter form of same. 
5. Middle whorls cancellated, basal whorl threaded sculpture only. 
6. Longitudinal sculpture strongest throughout. 
Platk XX. 
PalndcMrlna proica Gould. 
Whorls angulated or tabulated above. 
Fig. 7. Surface smooth, upper portion of whorls angulated. 
8. Surface smooth, strongly angulate (unique example). 
9. Eobust form slightly angulated above and faintly threaded. 
10. Rather slender form, strongly angulated and conspicuously threaded. 
11. AVhorls flattened or tabulated above, an<l faintly threaded throughout 
(unique example). 
12. Whorls angulated above, basal and penultimate whorl, faintly threaded. 
The two whorls above these sculptured both ways; the mouth rimmed 
and reflected (a very rare form). 
Pl.ATK XXL 
P(thidei<triii<i jirolca- Gould. 
Fig. 13. Whorls angulated above and exhibiting the two systems of sculpture, which 
in the middle whorls are subnodose at points of crossing. , 
14. Longitudinal sculpture strongest; plications on middle whorls less numer- 
ous and farther apart than on basal whorl. 
15. Short form, with strongly latticed sculpture on principal whorls. 
16. AVhorls angulated above, sculpture like middle whorls of thirteen. 
17. Robust form, angulated above, faintly threaded; longitudinal sculpture 
consisting of rather inconspicuous rounded swollen plications. 
18. Robust, angulated above, the middle of the whorls sculptured both ways, 
the lower part of basal whorl faintly sculptured transversely. 
The various examples above figured are connected by an endless chain of inter- 
mediate forms. 
