88 DISCOVERY REPORTS 



THE TROCHACEA 



The radula 



The Rhipidoglossid radula is undoubtedly one of the most difficult to interpret owing to the large 

 number and the intricate overlapping of the teeth. In the Calliostomid radula in particular, long, 

 slender, foliated cusps form a complicated network that effectively obscures the form of the bases of the 

 individual teeth unless these teeth are laboriously segregated on the slide. Even then it is difficult to 

 estimate the outlines these teeth would present when viewed from above in their natural working 

 position. Each angle from which an individual tooth is observed gives a different result, especially 

 with the laterals. 



I have achieved the best results, where there is sufficient material, by mounting several radulae — 

 one stained with eosin and mounted in Canada balsam, one unstained and mounted in glycerine jelly 

 and one or more in either medium with individual teeth and groups of teeth segregated from the mass. 

 Staining is essential to bring out the form of the base, but by this method the elaborate foliated cusps 

 so characteristic of the Calliostomids are not easily seen. On the other hand, glycerine jelly brings out 

 detail of the cusps to perfection but shows little else. 



In general terms the dental formula of the Trochacea consists of a central tooth, four to sixteen 

 laterals (usually four to five) and a large number of marginals (usually too many to count with accuracy 

 (expressed as oo)). The inner marginal in the Calliostomidae is always massive and clearly the most 

 effective working tooth. The rest of the teeth are so delicate that they can scarcely be operative in 

 mastication. 



The radula types covered by the present material are as follows : 



A. Marginal teeth very numerous. 



a. Central and laterals with long, slender, foliated cusps. 



aa. Inner marginal massive, crooked, with cusps on lower edge. Calliostomatinae 



b. Central and lateral teeth with short denticulated cusps. 



bb. Inner marginal not noticeably larger or more massive than neighbouring ones 



Stomatellinae = Margaritinae 

 Transverse rows forming a simple arc Margarites 



Transverse rows with a slight dip at the middle Margarella 



B. Marginal teeth few (5-10). 



Transverse rows with a pronounced dip at the middle. Solariellinae 



The epipodial processes 

 Interesting confirmation of differences shown by study of the Trochoid radula is shown by the 

 tentacles or filaments associated with the epipodial fringe. 



Calliostoma Swainson, 1840 (type: Calliostoma zizyphinum (Linn.) England). 



Two long, slender cephalic tentacles with the' eyes at the extremities of a pair of short tentacles, each 

 close against the outer side of the base of one of the long tentacles. Epipodial tentacles, three on each 

 side of the foot, long and slender (see Forbes & Hanley, 1851, 3, pi. EE and Fischer, 1887, p. 826, 

 fig- 585)- 



1. Calliostoma modestulum Strebel. Two long slender cephalic tentacles and eyes as in Calliostoma 

 typical. Epipodial tentacles four on each side of the foot, long and slender (Fig. D, 1). 



Dall (1889 a, p. 343), in describing C. platinum, 414 fathoms, California, stated that there were four 

 moderate-sized epipodial ' filaments ' and that the tentacles were long and slender. 



