298 Mr Jenyns's Monograph on the 



I may here observe that this, and all the other species of this 

 family breed readily in confinement, during the spring and summer 

 months. They are probably ovoviviparous ; and the young appear to 

 remain for a certain period within the folds of the branchiae previous to 

 their exclusion, since many may be found of different sizes within the 

 parent at one and the same time. They have the faculty of producing 

 long before they are arrived at their full growth, and even some indi- 

 viduals which are themselves so immature as to possess hardly any of 

 the distinguishing characters of the species, frequently contain young of 

 a sufficient size to be seen from without through the transparent valves. 



In distinguishing this and the last species, authors have frequently 

 drawn their essential characters from the presence and number of the 

 longitudinal, or as they term them transverse grooves, indicative of 

 the different stages of growth. But as these are very uncertain marks, 

 depending upon age and other circumstances, I have not thought it 

 necessary to notice them at all. The colour is not less variable. 



Sp. 3. C calyculata, Draparnaud. 



C. testa subrhombea, compressa, tenui, albo-lutescenti, diaphana, ; na- 

 tibus prominentibus, acutiusculis, tuberculosis. 



Long. 5\ lin. Alt. 4^ lin. Crass, vix 3 lin. 



Cyclas calyculata, Draparn. 130. t. 10. f. 13, 14. — Lamarck, 5. 559- 

 Pfeiffer, 122. t. 5./. 17, 18.— Nilsson, 99— Turt. Man. 14./ 3. 



Cardium lacustre, Montagu, 89. 



Tellina lacustris, Linn. Trans. 8. 60. — Turt. Conch. Diet. 180. 



Cyclas lacustris, Turt. Conchy! . Brit. 249. t. 11./ 18. 



Var. (3.— Tab. xix. Fig. 1. 



Testa orbiculato-rhombea, minus compressa, subdiaphana, fusco-ru- 



fescente. 



Lonff. 4i lin. Alt. 4 lin. Crass. 2| lin. 



