BRACHIOPODA 



179 



ORDER II. TELOTREMATA 



The peduncle-opening is confined to the ventral valve 

 in the adult, and is either at the umbo or beneath it. A 

 deltidium is developed, and a brachial skeleton is present. 

 E.g. Magellania. 



Spirifer (fig. 82). Shell transverse, more or less triangular, 

 biconvex, smooth or ornamented with ribs or strise. Often with a 



A B 



Fig. 82. Spirifer striatus, Carboniferous. A, interior of dorsal valve, 

 showing brachial skeleton. B, interior of ventral valve, showing 

 muscular impressions, area, and delthyrium. (From Woodward.) 

 x i 



sinus on the ventral valve and a ridge on the dorsal. Hinge-line 

 straight, generally long. An area on each valve, the ventral one 

 triangular, often transversely striated, with a delthyrium which is 

 partly closed by a deltidium ; dorsal area small. Teeth supported 

 by dental plates. Brachial skeleton often filling a great part of the 

 interior of the shell, formed mainly of two spirals, with their apices 

 directed laterally. Silurian to Permian. Ex. S. striatus, Carboni- 

 ferous Limestone. The sub-genus Martinia includes smooth forms 

 (e.g. S. glaber). 



Spiriferina. 



in the ventral valve 



Similar to Spirifer, with a high median septum 

 Devonian to Lias. Ex. S. walcotti, Lias. 



Syringothyris. Similar to Spirifer, but with a high area 

 and an internal tube in the delthyrium. Carboniferous. Ex. S. 

 cuspidata. 



12—2 



