XVI 



EULAMELLIBRANCHIATA — PHOLADACEA 



457 



narrow ; shell equi valve, long and narrow, gaping at both ends, 

 with periostracum, umbones flattened, ligament external, hinge- 

 teeth variable. ? Devonian . GenQvsi: Solecurtus, Phai-ella^ 



Pharus, Cultellus^ Siliqua, Unsis, Solen, 

 Orthonota (?), Palaeosolen (?). 



Fam. 4. G-lycimeridae. — Pedal orifice 

 very narrow, siphons long, united in great 

 part, often covered with periostracum ; 

 shell more or less equivalve, gaping at 

 both ends, hinge toothless or with two 

 weak cardinals, ligament external ; animal 



free or perforating. Cretaceous . 



Genera : Glycimeris^ Saxicava^ Cyrtodaria. 



Fam. 5. G-astrochaenidae. — Foot 

 small, cylindrical, no byssus, branchiae 

 narrow, siphons long; shell perforating 

 or cemented to a shelly tube, gaping 

 widely on the anterior and ventral sides, 

 no hinge-teeth, a deep pallial sinus. Cre- 

 taceous . Genera : G-astrochaena, Fis- 



tulana (tube with a median diaphragm, 

 perforated by the siphons). 



Sub-order VI. Pholadacea. — Man- 

 tle edges largely closed, siphons long, 

 united, foot short, truncated, disc-shaped, 

 ligament absent, two adductor muscles; 

 animal perforating. 



Fam. 1. Pholadidae, — Organs con- 

 tained within the valves, ctenidia pro- 

 longed into the branchial siphon, shell 

 more or less gaping, thin, dorsal margin 

 in part reflected over the umbones, one 

 or more dorsal accessory pieces, no hinge- ^^^ sio.- Teredo navaiis 

 teeth, an interior apophysis proceeding 



from the umbonal cavity. Jurassic . 



Genera: Pholas, Talona^ Pholadidea 

 (posterior extremity of the valves prolonged by a corneous 

 appendage, a passage to the long tube of Teredo')^ Jouannetia^ 

 Xylophaga^ Martesia; Teredina (Eocene). 



Fam. 2. Teredinidae. — Animal vermiform, ctenidia mainly 



L. : V, valves of shell ; 

 T, tube; P, pallets; SS, 

 siphons. (After Mobius.) 



