400 MOLLUSCOIDEA phylüm v 



Basiliola Dali. Deep-sea forms resembling Hemithyris, but with the 

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



Frieleia Dali. Resembling Heynithyris, but with a small dorsal spondylium. 

 Recent ; American Pacific. 



Atretia Jeffreys (Cryptopora Jeffreys 1869, non Cryptoporus Motoch 1858; 

 Neatretia CEhlert). Small, smooth sbells with an acute and 

 prominent open ventral beak. Dental plates and a high, 

 mesially situated, dorsal septum present. Recent. 



Subfamily C. Acanthothyrinae, novum. 



Ehynchonellids with a spinöse surface. 



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

 (Schioth.). Middie tfiyns, Dut witü well-developed dental plates. Jurassic to 

 pSifate'^'"^'^^^'' Recent ; Europe and Japanese sea. 



Fio. 595. 

 Acanthothyris spinosa 



Superfamily 2. TEREBRATULAOEA Waagen. 



Specialised Telotremata with the brachia supported hy calcareous, primitive or 

 metamorphosed loops. Shell strudure always pundate. Devonian to Recent. 



Division A. Terebratuloids. 



Terebratulacea with the loops unsupported hy 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 dired and composed of two 

 descending lamellae, uniting in the median 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 f amilies. 



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- 

 angulär, mesially ridged plate. Hinge- 

 plate perf orate. Devonian ; North America, 

 Amphigenia Hall (Enantiosphen Whid- 

 borne). Elongate-ovate, high-shouldered 

 Shells without median fold or sinus. 

 Fig. 596. *' Surface with concentric growth varices 



Centronella glansfagea (Hall). Devonian ; Brie and f aint radial Striae. Dorsal Valve with 

 County, N.Y. ^, £, Profile and dorsal aspect, ^/.. ^ ■, i . i • i j_ j- j_ ^ 



c, Loop, eniarged. a large sub-quadrate ninge-plate periorated 



by the visceral foramen and without a 

 cruralium. Middie Devonian; North and South America, France and 

 Germany. 



Eensselaeria Hall. Ovate or elongate-ovate striate Terebratuloids. The 

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



