APPENDIX. C51 



Vol. ii. p. 44G. Genus CYRENA. 



Mr. Deshayes has indicated a group of this genus under the 

 name of Anomala, but as this name is already in use, we would 

 suggest the following. 



Sub-gen. egeta, H. and A. Adams (Anomala, Desk., not Koppe). 



Shell ventricose, thin, anterior side short; posterior side pro- 

 duced and sub-rostrated. C. angulata, anomala, Cumingii, in- 

 fiata, insignis, isocardioides, and nitidula are examples. 



Vol. ii. p. 4=7(3. Genus CYAMIUM. 



We had considered the genus Turtonia to be the same as 

 Cyamium, but the shell of the former is closed at both ends, the 

 ligament is more exposed than in Cyamium, and it is also pro- 

 vided with slightly-prominent, elongated lateral teeth, which are 

 absent in Cyamium. The genus Turtonia should therefore be 

 kept distinct. T. minuta is the only species. 



The animal of Cyamium, as thus restricted, is unknown. The 

 shell may be described as equivalve, inequilateral, thin, slightly 

 gaping ; hinge with two cardinal teeth in each valve, no lateral 

 teeth ; ligament double, cartilage in a triangular groove behind 

 the teeth in each valve. 



Vol. ii. p 500. Genus MONOCONDYLiEA. 



Mr. Lea has described a sub-genus of Monocondylcca, under 

 the following name, the type of which, M. isocardioides, Lea, 

 is from the rivers of South America. 



Sub-gen. plagiodon, Lea. 



Shell inequivalve, obliquely trigonal, ventricose. Hinge with 

 the cardinal teeth crenulated, compressed, transverse, double 

 in each valve. 



Vol. ii. p. 51 2. Genus MYTILUS. 

 Sub-gen. stavelia, Gray. 

 Shell inequivalve, the ventral edge sinuous. M. tortus is an 

 example. 



