186 Mr. L. Reeve on the History, Synonymy, and 



46. Terehratula {Argiope) Neapolitana, Scacchi, Oss, Zool. ii. 

 p. 18; Conch. Icon. pi. 10. f. 45. 



Terehratula seminulum, Philippi. 

 Orthis NeapoUtana, Philippi. 

 Argiope NeapoUtana, Davidson. 

 Forbesii, Davidson. 



Hab. Mediterranean (at depths of from 60 to 100 fathoms) ; 

 Canaries. 



Of a more triangular form than the preceding species, while 

 the valves are plicately indented at the margin in rather a cha- 

 racteristic manner, the radiating ribs being arranged in three 

 fasciculi, or as it were on three shields. The apophysis is the 

 same as in A. cuneata ; but the margin of the valve is more 

 thickened internally, and between it and the loop there is a 

 distinct row of spinous teeth. 



47. Terehratula [Argiope) cistellula, Searles Wood, Ann. and 

 Mag. Nat. Hist. vi. p. 253 (fossil) ; Conch. Icon. pi. 10. f. 46. 



Megathyris cistellula, Forbes and Hanley. 

 Argiope cistellula, Davidson. 



Hab. Mediterranean and British Seas. 



This little species, originally discovered by Mr. Searles Wood 

 in a fossil state, has been found alive in the British seas at Zet- 

 land, in Belfast Bay, and at Exmouth, on the coasts of Guernsey 

 and Normandy, and lastly in the Mediterranean, which is the 

 specific home of the group. 



Subgenus 12. Thecidea, Defrance. 

 Apophysis callously affixed to the bed of the valve. 



48. Terehratula ( Thecidea) Mediterranea, Risso, Eur. Merid. pi. 4. 

 f. 183. 



Thecidea testudinaria, Miclielotti. 

 spondylea, Scacchi. 



Hah. Mediterranean (attached to corals). 



Thecidea is rather a difficult subject to observe, by reason of 

 its habits. It bears much the same relation to the rest of the 

 Terehratula that Hinnites bears to Pecten. The pedicle, like the 

 byssus in that genus, loses its function and is dispensed with, 

 and the animal affixes itself by the shell. The shell, as in most 

 such instances, is of veiy callous and irregular growth, and it is 

 only by the casual development of its structural details in a 

 numerous series of specimens that its characters can be ascer- 

 tained. In some fossil forms of Thecidea a minute terminal fora- 



