SPIRIFERID^. 321 



CYRTiA, Dalman, 1828. Shell impunctate, p^^ramidal, beak 

 prominent, area equiangular, deltidium with a small tubular 

 foramen. Fossil, 10 sp. Silurian — Trias ; Europe. S. trapezoid- 

 alis, Dalman (cxxxvii, 3 '. 



MARTINIA, M'Coy, 1844. (Ambocoelia, Hall, 1860.) Dorsal 

 margin shorter than the width of the shell, the angles of the 

 hinge-margin shortly rounded ; surface smooth ; spiral lamellae 

 small. Silur.— Carb. ; Eur., U. S. S. glaber,Sowh. 



SUESSIA, Deslongehamps, 1855. (Dedicated to M. Suess.) 

 Shell like Spirifer; texture fibrous; hinge-area wide as the 

 shell ; foramen deltoid ; large valve with two cardinal septa, and 

 a. prominent central septum, supporting a little plate; small 

 valve with a trilobed cardinal process, and a broad four-partite 

 hinge-plate, with processes from the outer angles of the dental 

 sockets ; crura of the spires united by a transverse band sup- 

 porting a small process. Fossil, 2 sp. Upper Lias ; Normandy. 

 S. imbricata, Desl. (cxxxvii, 1, 2). 



SYRiNGOTHYRis, Wiuchell, 1863. Shell like that of Spirifer, 

 with an elongated hinge-line. Ventral valve with a broad mesial 

 sinus, a very broad area, and a narrow triangular fissure closed 

 towards the apex by an external convex pseudo-deltidium ; 

 beneath which, and diverging from it, is another transverse plate 

 connecting the vertical dental lamellae, which are incurved so as 

 to nearl}^ join their inferior edges, thus forming a fissured tube, 

 which projects beyond the limits of the plate from which it 

 originates into the interior of the shell. A low median ridge 

 extends from the beak to the anterior part of the valve. Dorsal 

 valve depressed, without an area, and with a distinct mesial fold. 

 Shell-structure punctate. Fossil, 2 sp. Carboniferous ; United 

 States, Ireland, Belgium. S. ty pa, WincheW (cxxxvii, 6). "Is 

 it not an abnornial Spirifer or Cj^rtia?" — Meek. 



CYRTiNA, Davidson, 1858. {Etym. — Modified from the diminu- 

 tive [Gyrtidium'] of Cyrtia.) Shell resembling Spirifer, but 

 without the vertical shelly plates which diverge from the 

 extremity of the beak. Interior of ventral valve with two con- 

 tiguous vertical septa, 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 dental 

 plates, as in Pentamerus. The fissure is covered by an arch- 

 shaped deltidium ; but in G. Demarlii 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 G. heterocUta and C. septosa. " Spiral coils having the same 

 position as in Spirifer, but the first two coils are connected a 

 little in front of the mid-length by an apparatus somewhat like 

 that of Spirigera, but not so complicated, A very slender process 

 springs upwards towards the central valve from each coil, and, 



