312 MOLLUSCOIDEA—BRACHIOPODA SUB-KINGDOM V 
Superfamily 1. STROPHOMENACEA. Schuchert. 
Primitive Protremata without spondylia and cruralia. Cambrian to Recent. 
\ Family 1. Kutorginidae. Schuchert. 
Primitive Strophomenacea with incipient cardinal areas, great delthyrium and 
very rudimentary articulating processes and deltidiwm. Cambrian. 
Kutorgina, Billings. K. cingulata, as redefined by Walcott, from the 
American Lower Cambrian, is the only species positively known to belong to 
this family. Schizopholis, Waagen, of the Lower Cambrian in India, and 
Volborthia, Moller, of the Ordovician, may also possibly find a place here. 
Family 2. Hichwaldiidae. Schuchert. 
Primitive or aberrant, rostrate Strophomenacea, with narrow lateral grooves and 
ridges for articulation. Delthyriwm closed by a concave plate (? deltidium). Pedicle 
emerging through the ventral umbone and moving with growth anteriorly by resorption 
through the shell, as in Siphonotretidae. Ordovician and Silurian. 
Eichwaldia, Billings. The single species of this genus has a smooth 
exterior. Ordovician ; North America. 
Dictyonella, Hall (Eichwaldia, auct.) Exterior surface of valves pitted in 
quincunx, resembling Zrematis. Silurian ; North America, England, Bohemia, 
and Gottland. 
Family 3. Billingsellidae. Schuchert. 
Strophomenacea with well-developed cardinal areas and deltidiwm. Cardinal 
process obsolete or very rudimentary. Articulation fairly well developed. Cam- 
brian. 
Billingsella, Hall and Clarke (Protorthis, H. and C.) This is the only known 
genus of the family, and contains a number of the oldest well-developed 
species of Protremata. Cambrian ; North America. 
Family 4. Strophomenidae. King.! 
Strophomenacea with well-developed cardinal areas, deltidium, chilidiwm, cardinal, 
and articulating processes. Ordovician to Permian. 
Rafinesquina, Hall and Clarke (Fig. 517). Shells normally concavo-convex 
dorso-ventrally. Striae alternating in size, and crossed by finer concentric 
growth lines. Muscular area of ventral valve consisting of two broad flabel- 
late diductor scars enclosing an elongate adductor. In the dorsal valve, the 
bilobed cardinal process is low; the posterior arborescent adductor scars 
well defined. Vascular and ovarian markings often well indicated. Ordovician; 
North America and Europe. 
1 [According to J. M. Clarke, a separation into groups of the genera here included under one 
family is advisable, according as the shell is normally convex, or reversed convex. The habit of 
reversion, originating in the unequal growth of the two valves, characterises a large number of forms, 
which stand in a notable degree in successive genetic relationships ; while their affinities with the 
normally convex forms are less palpable. This author is in favour of restricting the Strophomenidae 
so as to include only those genera in which the shell is usually reversed convex, and employing the 
family term Leptaenidae for those having normally convex shells, —TRANS.] 
