34 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



crabs, and the locality, Swedish sea, where eplii'pjnum is not found. 

 There is no distinction between the smooth and aculeate forms : 

 I have taken wholly smooth, wholly aculeate and intermediate forms 

 on the same Chlamys ojjercularis ; nor can I find any essential 

 difference in other varieties, such as cylindrica, Gmelin, from the 

 arm of a crab Inachics. It is at once distinguished from all other 

 Anomiidae by the gills, which have no ascending lamellae (PI. I, f. 5). 

 Two muscular scars in the upper valve, small adjacent but distinct 

 (PI. I, f. 12), not showing the radial furrows of Monia. The byssal 

 plug is thin brown striate, as in Monia and quite difierent from that 

 of Anoyyiia. Jensen further points out (Danish Tngolf Exp., ii, 5, p. 1) 

 that the notch of this species is small and ov^l and the umbo almost 

 or entirely marginal, while the notch in 'patellij'ormis is large and 

 triangular and the umbo always a little way off the margin. 



EXPLANATION OF PLATE I. 

 Sections of Gill. (Diagrammatic. Dots indicate ciliary junctions.) 

 Fig. L Anomia ephippium. X 5. 

 ,, 2. Monia patdliformis. X 5. 

 ,, .3. M. squama, x 5. 

 „ 4. M. squama var. crassa. x 5. 

 ,, 5. Heteranomia squamula. Diagram of gill, x 5. 

 ., 6. H. squamula. Right side mantle removed, showing reduced gill. 



X 3/2. 

 „ 7. //. squamula. Left side, mantle removed. X 3/2. 



Outlines of Muscular Scars in Left Valve. 

 Fig. 8. Anomia ephippium. Poole. 

 „ 9. Monia patdliformis. Firth of Forth. 

 „ 10. M. squama. Oban. 

 „ IL M. sqicama YSiV. crassa. Eddystone. 

 „ 12. Heteranomia squamula, Brighton. 



Shells. 

 Figs. 13-18. — Monia squama \&v. crassa. Eddystone. 



I 



