BEACHIOPODA. 



38t 



valye ■^'ith a bi-lobed cardinal process, between the dental 

 sockets, and four depressions for the adductor muscles. 



Fio;. 184. 



Dorsal valve. 



Ventral valve. 



Interior of »S. rhomboidahs, var. annloga, Carb. limestone (after King). 

 e, foramen ; t, teeth ; o, ovarian spaces ; b, brachial pits ? 



There are no apparent brachial processes in the dorsal yalvo 

 of Strojjhomena, and it is possible that the sj^iral arms may have 

 been supported at some point near the centre of the shell {h) as 

 in Frodudus ; S. rliomboidalis occasionally exhibits traces of 

 spiral arms, in the ventral valve. 

 >S'. latissima, Bouch., has plain 

 areas, like Calceola. 



The valves of the Strophomenas 

 are nearly fiat until they approach 

 their full growth, they then bend 

 abruptly to one side ; the dorsal 

 valve becomes concave in >S'. alter- 

 nata and rliomboidalis, whilst in 

 B. jplanumhona and eugJypha it 

 becomes convex : these distinc- 



tions are not even sub-generic. 



Fig. 18.- 

 A, hinge-areas ; 



Lcpta:na, 2.. 

 , ventral ; b, interior 



of dorsal valve. 



Lower Silurian — Carb. North America, 



Fossil, 129 species. 

 Eui^ope, Thibet. 



S. demissa, Conr. (Strophoodonta, Hall), S. Dutertrii, and 

 several other species have a denticulated hinge-line. 



Sub-genera ? Lejjtcena (part), Dalman. L. transversalis, 

 Pig. 185. (Plectambonites, Pander.) Valves regularly curved; 

 dorsal concave, thickened, muscular impressions elongated. 

 Fossil, 41 species. Lower Silurian — Lias. North America and 

 Euroi^e. The lias Lejptcenas resemble Tliecidia internally; they 

 are free shells, with sometimes a minute foramen at the apex of 

 '^he triangular deltidium ; L. liassina, PI. XV., Fig. 25. 



Koninckia, Sucss. Producta Leonhardi, Wissm. (P. aljoina. 

 Schl.), Fig. 186. Trias, St. Cassian. >SAc/i orbicular, concavo- 

 convex, smooth ; valves articulated ? closely appressed ; ventral 

 valve convex, dorsal concave ; beak inciu'ved, no hinge-area 



