68 BRITISH CARBONIFEROUS BRACHIOPODA. 



Therefore Cyrtia, of Dalman, presents no other feature by which it can be separated from 

 Spirifer proper, than that of its deltidium and foramen, which are characters of hardly 

 sufficient importance to warrant the creation of a separate genus. 



In our British carboniferous rocks, the only two forms known to me that could be 

 referred to Dalman's Cyrtia are the 8. cuspidata and S. disians. 



In Cyrtina, the diverging plates already described do not exist, but we find in the 

 interior of the ventral valve (of C. heterodyta and C. septosa), two contiguous vertical septa 

 (PI. XIV, figs. Q, 7, 8), which 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 

 Petitamertis. 



The fissure is covered by an arch-shaped deltidium ; but, in C. Demarlii, Mr. 

 Bouchard has remarked that the median septum is continued as far as the under surface 

 of the deltidium, and the dental plates are fixed to the sides, instead of the upper edge as 

 in C. heterodyta and C. septosa. The arrangements in the smaller or more important 

 valve are still unknown, notwithstanding the many efforts I have made to pry into their 

 interior; and it is certain that no vestige of spiral coils have hitherto been noticed by any 

 author. Therefore, although we possess no proof that these three species of Cyrtina were 

 possessed of spirals, and consequently true Spiriferid^, it will be necessary to pause 

 before admitting the shells in question into the genus Fentamerus. 



Cyrtina septosa, Phillips. PL XIV, figs. 1 — 10, and PL XV, figs. 1, 2. 



Spikifera septosa, Phillips. Geol. of Yorkshire, vol. ii, p. 216, pi. xi, fig. 7, 1836. 



— suBCONicus, Be Koninck. Animaux Fossiles de la Belgique, p. 255, pi. xii, 



his fig. 5, a, b, c, 1843 {not Anomites subconicus, Martin, 1809). 



Spec. Char. Very transverse, somewhat lozen-shaped ; hinge-line as long as the 

 greatest width of the shell ; ventral valve moderately convex, subpyramidal, with a narrow 

 sinus extending from the extremity of the beak to the frontal margin. Area very large, 

 triangular, slightly curved upwards, and at an obtuse angle to the plane of the dorsal 

 valve, the beak not protruding beyond or above the angular extremity of the area ; fissure 

 large, deltidium (?). Dorsal valve semicircular, convex, divided by a narrow, slightly 

 elevated mesial fold, surface of both valves ornamented by from forty to seventy small 

 angular ribs, which increase in number from bifurcation as well as intercalation as they 

 proceed from the beaks to the frontal margin ; six or seven of these form the mesial fold, 

 and about a similar number that of the sinus, the radiating ribs being likewise intersected 

 by numerous concentric lines or laminjE of growth. 



