34 BRITISH CRETACEOUS BRACHIOPODA. 



are irregularly waving ; the few central ones extending almost in a direct line to the front, 

 but the lateral costae, particularly in older shells, seem to lie more against the central ones, 

 and augment rapidly by bifurcation and intercalation at different distances and periods of 

 growth. All we know of its interior is, that the valves articulate by the means of two 

 teeth in the larger and corresponding sockets in the smaller valve ; the beak seems to be 

 hollow, and strengthened by two slender plates situated at the base of the teeth, and 

 dividing it into three unequal partitions, as may be seen by the section I have given of the 

 beak at half its length (PI. Ill, fig. 25) ; these Plates, however, seem gradually to 

 approach the lateral portions of the beak, leaving the foramen entirely surrounded by its 

 substance and deltideum, as seen in fig. 28; in the interior of the smaller valve the boss or 

 cardinal muscular fulcrum, fig. 27'', is somewhat produced, and a short elevated longi- 

 tudinal septum extends to less than half the length of the valve. Whether the loop was 

 simply attached to the crural base, as in true Terebratulce, or doubly attached as in 

 Terebratetta, or otherwise disposed, is still a matter of conjecture. 



Ter. lyra has hitherto been found but in a few localities; viz., in the Upper Green 

 Sand at Chute Farm, near Horningham, where it is far from being common ; also still 

 more rarely in the Chalk, with green grains, of Chardstock, in which locality it was 

 discovered by Mr. Bunbury, some years ago. On the Continent it is found in the Upper 

 Green Sand, or Chloritic Chalk of Cap la Heve, near Havre, whence no doubt the first 

 specimen, figured in 17S9 in the 'Ency. Meth.,' was obtained. 



All our illustrations in PL III are from specimens belonging to the Upper Green 

 Sand from the neighbourhood of Warminster, figs. 17, 18, 19, 20, belonging to the 

 Collection of Mr. Falkner, of Devizes ; fig. 26 from that of Mr. Cunnington. 



Genus — Terebratulina, If Orb. 1847. 



Animal fixed to submarine bodies by means of a pedicle passing through the 

 foramen of the beak in larger valve, edges of the mantle free, body small. Shell 

 punctuated, inequivalve, variously shaped, generally longer than wide, and more or less 

 oval ; beak obliquely truncated by the foramen, which is large, and extending to the umbo 

 deltideum often small and indistinct ; smaller valve less convex than the perforated one, 

 with two more or less developed auricle expansions. Surface generally striated or 

 costellated. Valves articulating by the means of two teeth in the larger, and sockets in 

 the smaller valve ; apophysary system short, not exceeding one third of the length of the 

 shell, and formed of two short stems simply attached to the extremity of the socket ridges, 

 which, after converging, are united by a lamella in the shape of a small square tubular 

 ring bent upwards in front ; on the sides of these are fixed the free fleshy arms of the 

 animal which extend to near the frontal margin, and bent back in the shape of a loop. 

 The outer edges are covered by long cirri. 



