132 SYNOPSIS OF AMERICAN FOSSIL BKACHIOPODA. [bull. 87. 



! Family EICHWALDllD.E Schucliert, 1893.i 



Primitive or aberrant, rostrate Strophoiuenacea, with narrow lateral 

 grooves and ridges for articulation. Deltbyriuni closed by a concave 

 plate ( ^deltidium). Pedicle emerging through the ventral umbone and 

 moving with growth anteriorly by resorption through the shell, as in 

 Siphouotretida?. 



Eichwaldia Billings, 1858. | Dictyonella Hall, 1867. 



1. Family BILLHSTGSELLIU.E Schuchert, 1893. 



Strophomenacea with well-developed cardinal areas and deltidium. 

 Cardinal process obsolete or very rudimentary. Articulation fairly well 

 developed. 



Billingsella Hall and Clarke, 1892. 

 Protorthis Hall and Clarke, 1892. 



2. Family STROPHOMENIDJ3 King, 1846. 



Strophomenacea with well-developed cardinal areas, deltidium, chi- 

 lidium, cardinal and articulating processes. 



2a. Subfamily Rafinbsquinin^ Schuchert, 1893. 



Leptsenacea Brauu, 1840; Orthisid* (partim) d'Orbiguy, 1847; Davidsonidje King, 

 1850; Davidsoniniu Gill, 1871; Strophomeninai (partim) Gill, 1871; Waagen, 1884; 

 Cadomellinse Munier-Chalmas, 1887 ; Leptaenidie Hall and Clarke, 1895. 



Strophomenoids with ventral valve convex and dorsal concave, except 

 in Strophonella. The relative form of the valves is the reverse of the 

 Orthothetinse. 



Kaflnesquina Hall and Clarke, ' Pholidostrophia Hall and Clarke, 



1892. 

 Leptsena Dalman, 1828. 



Leptagonia McCoy, 1844. 

 Strophomena Meek, 1873 (not Blain- 



ville, 1825). 

 Plectambonites (Ehlevt, 1887 (not 

 Pander, 1830). 

 Stropheodonta Hall, 1852. 

 Brachyprion Shaler, 1865. 

 Douvillina CEhlert, 1887. 

 Leptostrophia Hall and Clarke, 

 1892. 



'In 1893 the writer referred this family with doubt to the Rhynchonellacea. The absence of crural 

 plates in Eichwaldia forbids that disposition. If the concave plate closing the umbonal pedicle 

 passage is a deltidium, there can be no doubt that this family belongs to the Protremata. Students 

 should search for the very young of Eichwaldia or Dictyonella, since it is through ontogeny alone 

 that the true systematic position of this family will be determined. 



1892. 

 Strophonella Hall, 1879. 



Amphistrophia Hall and Clarke, 1892. 

 Cadomella M.-Chalmas, 1887. 

 Leptella Hall and Clarke, 1892. 

 Plectambonites Pander, 1830. 



Leptiena Davidson, 1853; QElilert, 

 1877 (not Dalman, 1828). 

 Leptaenisca Beecher, 1890. 

 Christiaiiia Hall and Clarke, 1892. 

 Davidsonia Bouchard, 1847. 



