ASTRALITM. 187 



Turbo than the other subgenera of Astralium ; I have no hesitation 

 in placing it in the division of Astral i am containing species without 

 cusps to the central teeth. Compare Troschel, Das Gebiss der 

 Schnecken, t. xxi, f. 1. 



Cyclocantha. Troschel has examined the dentition of "A. rhodo- 

 xtnina" His figures show very nearly the same form that I have 

 figured for .4. Americanum, and especially in the central teeth. I 

 have examined the radula of only one species, A. plicatospinosum, 

 and find it of a wholly different form. (PI. 61, fig. 14.) The median 

 teeth do not have a basal plate projecting above ; the body is quad- 

 rangular, somewhat the shape of a maltese cross, without cusp. The 

 laterals have long cusps with spurs at their bases. I am inclined to 

 believe that Troschel's figure was drawn from a species of the West 

 Indian group of Astralium, not the real Cyclocantha. In view of 

 the great discrepancy between his results and my own, it is very de- 

 sirable that additional species of Cyclocantha be examined. 

 I 'I'dtiilla. Radula unknown. 



Cookia. My knowledge of the radula of this form is derived from 

 a figure and description given by Hutton. Median tooth with a 

 long basal plate and short body, of the general form shown on pi. 61, 

 fig. 11 for Pomaulax. It bears no cusp, and has small supporting 

 wings. The first lateral also is much like that shown in Pomaulax; 

 the others bear cusps, and, except the outer, have "stutzlamelle" 

 Inner marginal very broad, with wide cusp. Cusps of outer mar- 

 ginals simple. 



Pomaulax. (pi. 61, fig. 11.) In A. uudosum I find much the same 

 type of dentition as Hutton has figured for Cookia. The median 

 teeth have long basal plates, and a cuspless body, with its lateral 

 margins produced into supporting wings. The inner lateral is quite 

 complex in structure ; its upper edge is not reflected, but seems 

 turned upward somewhat ; its outer upper angle, a, lies under, and 

 its supporting wing ("Stutzlamelle "), b, over the succeeding lateral 

 tooth. The three following laterals have the same form of body, 

 but their apices bear broad simple cusps ; the outer lateral is narrow, 

 with a bidentate cusp. The marginals offer no unusual characters ; 

 the inner ones are large, with long cusps denticulate at their bases ; 

 the outer ones have serrate margins. 



Pachypoma. Median tooth with a narrow basal plate, projecting 

 above a rectangular simple accessory plate, which bears about the 

 middle the oval body, without cusp, but with the sides produced into 



