ECARDINES TESTICARDINES. 585 



genera which first appeared in the Cambrian have persisted to the 

 present day. 



Order 1. ECARDINES (!NARTICULATA).* 



Shell without hinge and brachial skeleton. Alimentary canal 

 with anus either ventral and to the right of the middle line, or 

 posterior and median (Crania). 



Fain. 1. Lingulidae. Shell thin, horny, almost equivalve, a long peduncle 

 passing between the two valves. Live in tubes in sand. Lingula Brug. ; 

 L. anatina Lam. ; Glottidia Ball. 



Fain. 2. Discinidae. Shell fixed by a peduncle passing through a hole in the 

 ventral valve. D-iscina Lam. ; D. atlantica King, 1330 fathoms, off West of 

 Ireland ; Discinisca Ball. 



Fam. 3. Craniidae. Shell orbicular, calcareous ; ventral valve adherent ; 

 without peduncle. Crania Retz. ; C. anomala Miiller, Loch Fyne. 



Order 2. TESTICARDINES (ARTICULATA).* 



The shell is calcareous, with hinge and brachial skeleton. The 

 intestine ends blindly. 



The exclusively fossil family Productidae, the edge of the shells of which 

 have no hinge, form the transition between the two orders. 



Fam. 1. Terebratulidae. Shell usually biconvex ; punctate, with complete 

 hinge ; beak of ventral valve perforated for short peduncle ; calcareous loop 

 bent back on itself. Waldheimia King (Figs. 461, 462), W. cranium Miill., 

 North British seas; Tcrebratula Brug., T. capsula Jeff., English Channel; 

 Terebratulina d'Orb., T. caput scrpentis L. Oban ; Tercbratella d'Orb., T. 

 Spitzbergensis Dav., N. British seas; Argiope Deslongchamps, A. decollata 

 Chemnitz, English Channel ; Cistella Gray (Fig. 459), C. cistellula S. Wood, 

 N. British seas, English Channel ; Megerlia King ; Kraussina Dav. 



Fam. 2. Thecidiidae. Shell plano-convex, usually fixed by beak of ventral 

 valve. Thecidium Defr. 



Fam. 3. Rhynchonellidae. Shell biconvex, hinge usually curved ; beak of 

 ventral valve incurved with foramen ; calcareous brachial supports as a pair of 

 short curved crura ; arms coiled in spiral. Rhyncliondla Fisch. (Fig. 463), 

 R. psittacea Gmeliu, N. British seas; Atretia Jeff., A. gnomon J. , west of 

 Donegal Bay in 1400 fathoms. 



* The localities mentioned in this list refer only to the places in the British 

 area, where the species have been obtained. They are taken from Shipley's 

 article in the C'amb. Nat. Hist. 



