TURBO. 185 



frequent in the Trochidce. They are made up of three parts, which 

 are lettered on my plate 61, fig. 12; the body of the tooth d, which 

 bears the cusp, e, when any is present ; this is usually expanded at 

 the lateral margins into supporting ivings, c, (the "Stutzlamelle" of 

 Troschel.) Under it lies the basal plate, a. ("Basalplatte" of 

 Troschel.) 



Between the body and the basal plate there is frequently an 

 accessory plate, marked b in the figure, the function of which is 

 unknown to me. 



Genus Turbo. 

 A. Central teeth without cusps. 



Turbo, including Senectus and Batillus. Troschel has figured 

 the raduhe of ten species of this group including, however, only one 

 of typical Turbo, T.petholatus ; and I have examined those of several 

 additional forms. There is but slight variation in the several species, 

 and for detailed descriptions of each the student is referred to 

 Troschel's work. The median tooth consists of a .narrow oblong 

 quadrate basal plate, frequently with accessory plates of various 

 forms, to the lower end of which is attached the oval body of the 

 tooth, a simple plate without cusp, bearing supporting wings at 

 the sides. (pi. 61, fig. 6, T. radiatus Gmel.). Frequently the 

 central teeth are asymmetrical in this group. The laterals bear 

 supporting wings at their outer angles, and are various in form, with 

 or without cusps; the inner marginals are very large, with large 

 cusps, (pi. 61, fig. 5, T. argyrostomus.) 



Callopoma. Median teeth like those of Turbo; laterals with 

 simple cusps, and, except the outer one, supporting wings, giving 

 the body of the tooth a trigonal form. Marginals as in Senectus. 



Xmella. Very similar to Callopoma in character. (See Troschel) 



Modelia, Ocana. Radula unknown. 



B. Central teeth ivith cusps. 



Marmorostoma. In this and the following subgenera the central 

 teeth have decidedly reflected simple cusps. The lateral margins 

 bear supporting wings. Lateral teeth similar, but asymmetrical, 

 the outer one without supporting wing; marginals as in Senectus. 

 (T. porphyrites, pi. 61, fig. 10.) Additional species are figured by 

 Troschel. T. smaragdus, which I include in this group, has similar 

 teeth, except that the basal plate projects above the cusps of median 

 and lateral teeth. 



