CYRTINA. 49 



Spirifer heteroclitus, Quenstedt. Handbuch der Petrefactenkunde, pi. xxxviii, fig. 21, 



1851. 



— — Davidson. General Introduction, pi. vi, figs. 63, 64, 1853. 



— — Schnur, in Dunk. u. Von Meyer's Palaeontograph., vol. iii, pi. xxxv, 



fig. 6, 1853. 



— — Sandberger. Die Brachiopoden des Rheinischen Schichtensystems 



in Nassau, pi. xxxii, fig. 8, 1855. 

 Cyrtina heteroclita, Dav. Mon. Carb. Bracb., p. 67, 1858. 



Spec. Char. General shape acutely pyramidal ; hinge-line as long as, or a little shorter 

 than, the width of the shell. Ventral valve pyramidal, and much deeper than the opposite 

 one ; area flat, triangular, very large, and bent back at various angles to the general 

 surface of the dorsal valve ; fissure long, narrow, and almost entirely arched over by a 

 pseudo-deltidium ; sinus deep, angular, extending from the extremity of the beak to the 

 front. Dorsal valve semicircular, with a prominent, more or less angular, fold. Each 

 valve is ornamented with from six to sixteen or more angular ribs. In the interior of the 

 ventral valve two contiguous vertical septa coalesce into one median plate, which extends 

 from the extremity of the beak to within a short distance of the frontal margin, and then 

 diverges to form the dental plates, in a very similar manner to what we perceive in 

 Pentamerus. The median septum is continued as far as the under surface of the 

 deltidium, although this is not always seen in our specimens. Shell-structure punctated. 

 Proportions very variable : 



Length 5, width 7, depth 10 lines. 



Obs. This important and characteristic fossil of the Middle Devonian limestones of 

 Great Britain and the Continent is exceedingly variable in shape, this being chiefly 

 occasioned by the greater or lesser development of the area, and of the number of ribs 

 with which the surface of the shell is ornamented. In some specimens the beak is also 

 twisted to one side or the other. It is a small species, but some French specimens 

 have attained twice the dimensions of any hitherto found in this country. In Devonshire 

 it occurs in Upper Devonian limestone, near Plymouth ; at Barton and Lurmnaton, near 

 Torquay ; Woolborough, near Newton Abbott ; Dartington, near Totness, and in coarse 

 limestone at Hagginton Hill, near Ilfracombe, North Devon. On the Continent it 

 is found at Ferques, in the Boulonnais (France); Chimay (Belgium); the Eifel, in 

 Nassau, &c. 



Var. multiplicata, Dav. PI. IX, figs. 11 — 14. 



Spirifera cuspidata, Phillips (uot of Sow.). Pal. Foss. of Cornwall, Devon, and West 

 Somerset, p. 72, pi. xxix, fig. 124 B . 



Spec. Char. Shell transverse, wider than long; lateral margins forming attenuated 

 acute angles with the extremities of the hinge-line or area ; dorsal valve semicircular. 



G 



