414 



MOLLUSCOIDEA 



PHYLUM V 



Fig. 027. 



A, B, Ptychospira ferita (von Buch). Devonian ; Gerolstein, Eifel. i/j. 

 D, RhyncJiospira scdteri (David.). Silurian ; Wenlock, Shropshire. C, In- 



commonly recurved, but is sometimes bifurcated. Shells plicate and their structure 

 abundantly punctate. Silurian to Permian. 



Bhynchospira Hall (Fig. 627, 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, ex- 

 panding apically and 

 terminating pos- 

 teriorly in an oblique 

 edge. Shell structure 

 punctate. Devonian 

 and Lower Carboni- 

 ferous; North America 



terior ofdorsa'l valve. D, Median vertical section through both valves, 3/^ g^nd EurODe 

 (after Davidson). ^ ' . 



Homoeospira Hall 

 and Clarke. Like the last, but dilFers in having a linear cardinal process 

 separating the crural plates. Jugum not apically expanded, but terminating 

 in an acute stem. Silurian ; North America. 



Ptychospira Hall and Clarke (Fig. 627, A, B). Like Bhynchospira, but with 

 a few angular plications. The jugum has a long, simple process passing 

 outward between the coils to near the inner surface of the ventral valve. 

 Devonian to Lower Carboniferous ; North America and Germany. 



Betzia King (Trigeria Bayle). Resembling Bhynchospira externally. The 

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

 terminally forked. This genus formerly contained all shells having a retzioid 

 exterior. At present, however, but a single species is admitted. Devonian ; 

 Europe. ^ 



Hustedia Hall and Clarke. Externally like Eumetria, 

 but with coarse plications, and internally with a split 

 tube, as in Betzia. Spirals and jugum similar to those 

 of EuwMria, but with fimbria and spinules respectively. 

 Upper Carboniferous and Permian; America, Europe, 

 India and China. 



Trematospira Hall. Transverse Bhynchospirae. Silu- 

 rian and Devonian ; North America. 



ParazygaHsÄlai.ndClsi.Yke (Fig. 628). Like Trematospira, 

 but with the fine, simple ribs covered with very delicate, 

 short, hair-like spines. Devonian ; North America. 



Eumetria Hall. Elongate terebratuliform shells with 

 numerous fine radiating Striae. Hinge - line short. 

 Dorsal hinge-plate very complicated. Jugum similar 

 to that of Betzia, but the terminally bifurcated process 

 is extended back ward at an abrupt angle, and termi- Pamzyga Ursuta (Haii). 

 nates just in front of the apices of the primary lamellae. tud?y!^T, shei°i"me natural 

 Shell structure punctate. Lower Carboniferous; North '^"*'- ^''«^"^e with dorsal 



Fig. 628. 



America and Europe. 

 Acambona White. 



Carboniferous : North America. 



valve partly broken open, 

 shovving spiralia. C, hinge- 

 line of ventral valve, enlarged 

 after Hall). 



