400 



MOLLUSCOIDEA 



PHYLUM V 



Basiliola Dall. Deep-sea forms resembling Ilemithyris, but with the 

 deltidial plates united into a spondylium-like plate. Recent. 



Frieleia Dall. Resembling Heinithyris, but with a small dorsal spondylium. 

 Recent ; American Pacific. 



Atrefia Jeffreys (Cri/ptopora Jeffreys 1869, non Cryptoporus Motoch 1858; 

 Ncatretia QChlert). Small, smooth shells with an acute and 

 prominent open venti"al beak. Dental plates and a high, 

 mesially situated, dorsal septum present. Recent. 



Subfamily C. Acanthothyrinae, novum. 



Bhynchonellids with a spinose surface. 



Acanthothyris d'Orb. (Fig. 595). In general like Hemi- 



Pm. 595. 



Amnthothyris spinosa ,7., ., ■,■, ^ ^ 11,11, 



(Sciiioth.). Middle t/iyns, but With well-developed dental plates 

 pS.tate!'''"''^^'^" Recent ; Europe and Japanese sea. 



Jurassic to 



Superfamily 2. TEREBRATULACEA Waagen. 



Specialised Telotremata with the brachia supported by calcareous, primitive or 

 metamorphosed loops. Shell structure always punctate. Devonian to Recent. 



Division A. Terebratuloids. 



Terehratulacea with the loops unsupported by a median dorsal septum at any stage 

 of growth. Brachial cirri directed outwards in larval stages. 



Family 1. Centronellidae Hall and Clarke. 



Primitive Terebratuloids with short loops developing direct and composed of two 

 descending lamellae, uniting in the mediayi line and forming a broad arched plate. 

 Shells smooth, faintly striate or rarely plicate. Devonian to Triassic. 



This family comprises the simplest of all Terebratuloids, and from it are probably 

 descended the other loop-bearing families. 



Centronella Billings (Fig. 596). Commonly small, smooth, plano-convex 



or concavo-convex shells, with the descend- 

 ing branches of the loop broadening 

 rapidly anteriorly, and uniting in a tri- 

 angular, mesially ridged plate. Hinge- 

 plate perforate. Devonian ; North America. 

 Amphigenia Hall (Enantimphen Whid- 

 borne). Elongate-ovate, high -shouldered 

 shells without median fold or sinus. 

 Surface with concentric growth varices 

 and faint radial striae. Dorsal valve with 

 a large sub-quadrate hinge-plate perforated 

 by the visceral foramen and without a 

 North and South America, France and 



Fig. 596. 



Cent ronelki glansfagea (RM). Devonian; Erie 

 County, N.Y. .1, B, Profile ;md dorsal aspect, Vi- 

 C, Loop, enlarged. 



cruralium. 

 Germany. 



Bensselaeria 



Middle Devonian ; 



Hall. Ovate or elongate-ovate striate Terebratuloids. The 



descending branches of the loop diverging for a short distance, thence acutely 



