050 APPENDIX. 



and more or less covered by a sunken tubercle in front. Disk 

 fringed. 



Ex. F. agglutinans, Lamarck (Novae-Zealandise, Gray). 



Sub-gen. arytene, Gray. 



Disk simple, not fringed. F. tuberculata is an example. 



Genus HUMPHREYIA, Gray. 



Animal attacking itself when young by the ventral edges of 

 the shell, and during its progress to the adult state extending 

 the valves behind into a tube. 



Ex. H. Strangei, A. Adams. 



Vol. ii. p. 353. Genus MYA. 



The sub-genus Platyodon of Conrad should be kept as a 

 distinct genus. We have recently had an opportunity of ex- 

 amining a specimen of P. cancellata and of confirming his 

 statement as to the siphonal orifices being furnished with tes- 

 taceous appendages. 



Genus TANYSIPHON, Benson. 

 (Fam. geauconomtid^;.) 



Siphons produced and united nearly to the ends, the ex- 

 tremity of the siphonal sheath and that of the branchial orifice 

 fringed. 



Shell inequilateral, transversely oblong, rounded at each end 

 and slightly gaping, covered with an epidermis ; beaks obtuse, 

 rather prominent. Hinge with three teeth in the right, and two 

 in the left valve. Pallia! sinus deep, extending to more than 

 half the length of the shell. 



Ex. T. rivalis, Benson, pi. 138, fig. 15. Shell, T. rivalis, 

 fig. 15, a, 15, b. 



This genus, which is allied to Glauconomya, is from the 

 vicinity of Calcutta, and was found buried in the mud at extreme 

 low-water. 



