330 MOLLUSCOIDEA—BRACHIOPODA SUB-KINGDOM V 
Sub-Family A. TRopImpoLEPritnak. Schuchert. 
Terebratellidae with the loop consisting of two slender descending branches, uniting 
with a high, vertical septum. Devonian. 
Tropidoleptus, Hall. Plano-convex plicated shells with a long straight 
and narrow cardinal area. Teeth and dental sockets corrugated on their 
outer surfaces. Devonian; America, Europe, and South Africa. 
Sub-Family B. MerGatTuHyrinar. Dall (emend, Beecher). 
Terebratellidae in which the loop is composed of descending branches only, passing 
in the highest genus through stages correlative with Gwynia, Cistella, and Megathyris. 
The lower genera do not complete the series. The original stock for the two following 
subfamilies. Jurassic to Recent. 
Gwynia, King. Minute, elongate-oval, smooth shells with a_ short, 
nearly straight hinge-line. Neither 
septa nor loop. Brachia primitive, 
consisting of a circlet of cirri. 
Recent. 
Zellania, Moore. Minute shells 
without a loop, but with a median 
septum in each valve. Lias ; Europe. 

Ui 
Fic. 556. : : 
Raster BiG. 557. Cistella, Gray (Fig. 556). Ex- 
Cistella bilocu- z! : ° 
laris, Desl. sp. Megathyris decollata, Chem. sp. ternally like Megathyris, but without 
Cenomanian ; La Recent ; Mediterranean. Interior 1, Hees aoe 5 
Manche. 1/;. of dorsal valve, 4/; (after Davidson). lateral septa. Cretaceous to Recent ? 
Europe. 
Megathyris, VOrbigny (Argiope, Deslong.), (Fig. 557). Transversely elon- 
gate, plicate, shells with long and straight hinge-line. Dorsal valve with 
three or five septa, causing the brachidium to have four lobes. Jura to 
Recent ; Europe. 
Sub-Family C. Datiintyar. Beecher. 
Terebratellidae with the loop composed of descending and ascending lamellae, 
passing in the 
highest genera 
through metamor- 
phoses comparable 
to the adult struec- 
ture of Platidia, 
Ismenia, Muehl- 
feldtia, Terebrat- 
alia, and Dallina. 
The lower genera 
« b] 
therefore, do not 
Muehlfeldtia truncata, Gemm. sp. A728 o final 
Recent; Mediterranean. Interior regimes to the final 
of dorsal valve (c, Crura ; d, Dental stages. Jura to 
sockets ; e, Jugum; f, 7, Ascending +, “ 
Muehlfeldtia pectunculus, Schloth.sp. Upper and descending branches of loop; Recent. Recent 
Jura; Engelhardsberg, Franconia. A-C, Shell p, Process attached to median cy SR 
of the natural size. D, EL, Two views of loop, septum ; pr, Cardinal process; 5, genera restricted 
enlarged. Median septum). to boreal seas. 

Fic. 559), 

Platidia, Costa (Morrisia, Davidson). Small, smooth, biconvex shells with 
