OIIDKH IV 



TELOTREMATA 



337 



Metaplasia, Hall and Clarke. Spirifer-\ike shells, with a median fold on 

 the ventral valve and a sinus on the dorsal valve. Lower Devonian ; North 

 America. 



Family 3. Athyridae. Phillips. 



Spiriferacea with tJie bases of the primary lamellae situated between the spiralia, 

 and sharply rer'urm/ i/<>r.wll>( nf fl/> // jinn-lion with the crura. Spiralia more or less 

 laterally directed. Jugum complete, V-shaped, with the apex drawn out into a simj)le, 

 bifurcated, or otherwise modified pi'ocess. Silurian to Trias. 



This large, chiefly Palaeozoic family, with its numerous highly differentiated species, 

 is divided into six sub-families, on the basis of the simplicity or complexity of the 

 juguni. These are the Rhynchospirinae, Hindellinae, Athyrinae, Diplospirinae, Koninck- 

 ininae, and Meristellinae. 



h'lii/nchospira, Hall (Fig. 578, C, D). Rostrate, radially plicate shells with 

 a short curved hinge-line ; apex truncated by a circular pedicle opening. 

 Dorsal hinge-plate like that of Trematospira. Spirals with from six to nine 

 volutions. Jugum V-shaped, expanding apically and terminating posteriorly 

 in an oblique edge. Shell structure punctate. Devonian to Lower Carboni- 

 ferous ; North America and Europe. 



Homoeospira, Hall and Clarke. Like the last, but differs in having a linear 

 cardinal 'process separ- 

 ating the crural plates. 

 Jugum not apically 

 expanded, but termi- 

 nating in an acute 

 stem. Silurian ; North 

 America. 



Ptychospira, Hall 

 and Clarke (Fig. 578, 

 A, B). Like Rhyncho- 

 spira, but with a few 

 angular plications. The FIG. 578. 



. c , r i . , A, Jl, Ptychospira ferita, von Buch. Devonian; Gerolstein, Eifel. 1/1- 



JUgUm naS a long Simple c, D, Rhynchospim Salteri, David. Silurian; Wenlock, Shropshire. C, In- 



terior of dorsal valve. 

 (after Davidson). 



D, Median vertical section through both valves, 



nrnnocs ecnrr rmf 



'" 



ward between the coils 



to near the inner surface of the ventral valve. Devonian to Lower Carbon- 



iferous ; North America and Germany: 



Retzia, King (Trigeria, Bayle). Resembling Rhijnchospira externally. The 

 ventral umbonal cavity has a split tube. The single process of the Jugum 

 terminally forked. Devonian ; Europe. 



This genus formerly contained all shells having a Retzioid exterior. At present, 

 however, but a single species is admitted. 



Hustedia, Hall and Clarke. Externally like Eumetria, but with coarse 

 plications, and internally with a split tube, as in Retzia. Spirals and jugum 

 similar to that of Eumetria, but with fimbria and spinules respectively. 

 Upper Carboniferous ; America, Europe, India, and China. 



Trematospira, Hall. Transverse Rhynchospirae. Silurian and Devonian ; 

 North America. 



VOL. I Z 



