•part 2] SYlilNGOTHYRIS AND SPIRIFERINA. 203 



Tylothyris subconica subcoxica (Martin) emend. (Text- 

 fig. 4 e, p. 199 ; PI. XIII, figs. 5 a-5 c.) 



1809. Conch ijliolith us anomites suhconicus Martin, ' Petvifacta Derbiensia ' 



pi. xlviii, figs. 6-8. 

 1858. Spii ifera subcoiiica Davidson [4J p. 48 & pi. i\', tigs. 3, 3 a, 3 h, 

 1!H)6. Syrinqothyris suhconica Vaughan, 'Rush Paper' [34] p. 311 & pi. xxx, 



'tig. 7. 



This subspecies includes the form upon which the species was 

 originally founded, since in the original account Martin described 

 his specimen as having an area ' which is straight, and not recurved 

 as in cusjiidatus.'' His figures also indicate a flat area. 



Description. — Shell spiriferoid, of medium size, twice as wide 

 as long, greatest width along the hinge-line, cardinal extremities 

 slightly produced. 



Pedicle -valve acutely pyramidal, cardinal area practically a 

 plane triangle, a little more than twice as wide as high ; plane of 

 the area at right angles to that of the brachial valve, its lateral 

 edges well defined and angular. Apical angle about 115°. 



Delthyrium twice as high as wide, delthyrial covering unknown. 



Lateral slopes slightly convex or nearly flat. Sinus angular, 

 sharply defined by angular ridges diverging at an angle of about 

 30°. The line along the floor of the sinus from the beak to the 

 anterior margin is very slightly curved or practically flat. 



Brachial valve slightly convex, nearly semicircular in outline. 

 Mesial fold distinct, low, and rounded ; its convexity decreases 

 towards the anterior margin, while that of the lateral slopes 

 increases in the same direction. 



Each lateral slope in both valves is ornamented by ten or eleven 

 simple angular costse of which the first six or seven on either side 

 are large and well developed, the remainder being short and incon- 

 spicuous and not apparent in exfoliated specimens. In some 

 specimens the costa? are slightly sinuous ; they are separated by 

 furrows approximately equal in depth and width to the costse on 

 each side of them. Surface of both valves, except the cardinal 

 area, marked by regular imbricating lamellae. 



Internal structures: — Pedicle -valve. — The delthyrial sup- 

 porting-plates extend across the cavity of the valve, and are 

 divergent. Median septum well developed, reaching' nearly to the 

 level of the area near the beak, becoming gradually lower, and 

 disappearing about half-way between the beak and the anterior 

 margin. The apical portion of the septum is embedded in the 

 apical callosity, which is well developed. 



In the brachial valve there is a low median septum extending 

 for about two-thirds of the distance from the beak to the anterior 

 margin. 



Shell-structure fibrous and impunctate. The dimensions of an 

 average specimen are as follows : — width along hinge-line, 36 mm. ; 

 length of brachial valve, IS mm. ; height of cardinal area, 1-5 mm. 



Holotype (of S. subconica suhconica). — A specimen from 

 Attermire, in my collection, now deposited in the National Museum 



