117 



112. trigona, Desk. 



113. triquetra, id. 



114. tuniida, Desk. 



115. turgicla, Lea. 118. ventricosa, Desk. 



116. Vanikorensis, Quoy. 119. violacea, Lam. 



117. variegata, D'Orb. 120. Woodiana, Lea. 



Figure. 



Cyrena fluminea. PI. 37. Fig. 198. Shell illustrative of a concentri- 

 cally ridged species, showing the two' extended lateral teeth. 



Genus 10. CYCLAS, Bruguiere. 



Animal; suborbicular, its mantle freely open in front and anteally 

 united posteriorly, to form a produced sip/ion, loliich is some- 

 times divided into two nearly equal tubes, edges of the mantle 

 and of the siphonal tubes not fringed. 



Shell; ovately globose, thin, covered with a slight olivaceous epi- 

 dermis; hinge composed of two small cardinal teeth, one of 

 which is bifid, in one valve, and one in the other, two rather 

 remote lateral teeth in each valve. 



The Cyrena, of the Tropics are represented in the boreal and subtem- 

 perate zones by a tribe of closely allied animals of very much smaller size, 

 some even minute, with thin, olive, horny shells. They include two sec- 

 tions, named respectively Cyclas and Pisidium. In the first the siphons are 

 separated ; in the second they are united in a sheath and the species are 

 smaller. In both the edges of the mantle and siphonal orifices are plain. 

 They live buried in mud in ditches and pools, or in gentle streams, 

 drains, etc. 



1. abdita, Hold. 



2. abrupta, id. 



3. acuminata, Pr. 



4. albula, id. 



5. altilis, id. 



6. amnica, Mull. 



7. argentina, D'Orb. 



8. auvea, Prime. 



9. australis, Phil. 

 10. Bahiensis, Spix. 



Species. 



11. bulbosa, Anth. 



12. cserulea, Prime. 



13. Canariensis, Shut. 



14. Capensis, Krauss. 



15. cardissa, Prime. 



16. casertana, Poli. 



17. castanea, Prime. 



18. Chilensis, D'Orb. 



19. cicer, Prime. 



20. compressa, id. 



21. consobrina, Feruss. 



22. constricta, Anth. 



23. contorta, Prime. 



24. cornea, Linn. 



25. Creplinii, Dkr. 



26. dentata, Hold. 



27. detrnncata, Pr. 



28. distorta, id. 



29. dubia, Say. 



30. duplicata, Pfeif. 



