24 
4. Aphrobita. 
1. A. grcenlandica, t. 329. f. 2. 
III. Foot elongate, cylindrical, tubular. 
Fam. 19. Thyasidoe. 
Mantle free beneath, with transparent oblique vessels. Siphons, 
two simple holes edged by the mantle. Foot cylindrical, annu- 
lated from the lower edge of the compressed body, attenuated at the 
tip. Gills one on each side, small, united together behind. Labial 
palpi none. 
1. Thyas. 
1. T. radula, t. 358. f. 4. 
IV. Foot compressed, truncated and dilated at the end for crawling 
and anchoring. 
Fam. 20. Ledadee. 
Gills small, oblong, subpinnate?, formed of separate threads. 
Lips large. Palpi very long, subulate. Siphons small, united. 
Shell equivalve. Hinge-teeth two, elongate, nearly parallel with 
hinge-margin, each divided into numerous transverse hook-like 
plates. Siphonal sear distinct, inflected. 
* Cartilage internal, triangular. 
1. Yoldia. 
1. Y. arctica, t. 372. f. 8. 
2. Y. australis (fig. 7). 
Fig. 7- — Yoldia australis (magnified). 
a a , adductor muscles, p p, pedal muscles, g, gills, s, siphon, t c, labial 
palpi and appendages, i, intestines, f foot, xx, lateral muscle of 
foot, m, mantle line. I , ligament. 
2. Leda. 
1 . L. caudata, t. 332. f. 2. 
2. L. minuta, t. . 
