140 



1. alba, Rang. 



Species. 

 2. transversa. Lam. 



3. rubra, Roissy. 



Figure. 



Ungulina transversa. PL 39. Fig. 217. Shell with one valve dropped 

 to show the central bifid tooth and ligamentary pit. 



Genus 4. MESODESMA, Deshayes. 



Animal ; with the lobes of the mantle united about two-thirds of 

 their length, open posteriorly for the passage of two short si- 

 phons ; foot flat, triangular, partially concealed by the branchiae. 



Shell ; ovate, transverse, or triangular, equivalve, rather thick, 

 compressed ; hinge composed of two lateral teeth in each valve, 

 between which is a deep triangular cavity containing the liga- 

 ment. 



Under Mesodesma we have a somewhat promiscuous series of shells of 

 rather solid pallid substance, distinguished by a hinge of corresponding 

 solidity. The ligament is contained in a conspicuous triangular cavity, 

 not obliquely curved, as in the two preceding genera, but perpendicular, 

 and the valves interlock on either side by strong lateral teeth. Some of 

 the species from New Zealand inhabit the sands of estuaries. 



1. arctatum, Gould. 



2. Chemnitzii, Desk. 



3. corneum, id. 



4. cuneatum, id. 



5. cycladum, id. 



6. deauratum, Hani. 



Species. 



7. donacillum, Desk. 



8. donacium, id. 



9. erycina, id. 



10. glabellum, id. 



11. glabratum, id. 



12. Jauresii, Joannis. 



13. planum, Hani. 



14. Quoyi, Desk. 



15. Solenoides, King. 



16. striatum, Desk. 



17. trigonum, id. 



18. triquetrum, Hani. 



Figure. 



Mesodesma NovjE-ZelandijE. 

 hinsce. 



PL 43. Fig. 233. 



Shell, showing the 



