GINGLYMACONCHA. MYAD. 267 
FAMILY V. MYAD. 
Mya, Auctorum. 
The shells generally inequivalve, gaping behind ; the hinge 
toothed only in the genera of the third Stirps: the ligament is 
either internal, and placed in either a horizontal or vertical pro- 
cess ; or external, and hinge-shaped. 
The tracheal or respiratory tubes are always much elongated, 
are joined together, and are covered by that epidermis which 
covers the shell: the mantle, in the first Stirps at least, is 
joined everywhere, excepting at the exit of the foot. 
Stirpium et Generum Synopsis. 
Stirps 1. Cardo edentulus; processu horizontali in valva simistra 
ligamentum elasticum aperiens ferente. 
Processu ligamentum ferenteinvalva f{ fixo .. 16. Mya. 
US Sa erage are mobili. 17. MaGpaAta. 
Stirps 2. Cardo edentulus ; processu verticali igamentum elasticum 
aperiens in valva utraque ferente. 
. externé prominens ginglymo- 
Ui Z WOES: GA Se: aes 18. THRActa. 
“ae ao omnino recon- { ineequalibus. 19. GALAXURA. 
| ditum ; valvis \equalibus .. 20. [xarTta. 
Stirps 3. Cardo dentatus ; processu verticali in valva utraque liga- 
mentum elasticum aperiens ferente. 
Cardo mm valva utraque pone ligamentum 
dente parvo lamelliformi; valva sinistra 
dente triangulari ante ligamentum imstructa 21. LuTRARta. 
Cardo in valva utraque ante ligamentum dente 
SR CRARACTUCHIS. wie d. oS il. Y atl. sitidn so « 22. PSAMMOPHILA. 
Cardo in valyé una dente uno recuryo, in al- 
tera dentibus duobus instructis.......... 23. ORONTHEA. 
IQ 
A 
