106 THE DEVONIAN OF MISSOURI. 



Ventral valve gibbous in the upper half, regularly curving to the front and sides; 

 sinus well defined, usually shallow and rounded, sometimes deep and angular, and much 

 produced in front ; beak small and incurved over the area, which is high and concave and 

 extending about half the entire width of the shell; foramen often limited by a sharp ele- 

 vated border, which appears to be a projection of the dental plates. 



Dorsal valve gibbous, regularly convex on the sides, a little flattened at the cardinal 

 extremities; mesial fold abruptly elevated in the lower part, often but little elevated or 

 scarcely defined in the upper part; beak small, slightly arched over the sublinear area, 

 which is somewhat concave. 



Surface marked by from three or four to eight or nine low, rounded, often obscure 

 plications on each side; these are crossed by imbricating lamellose striae, which are 

 sometimes wide or distant, and often crowded. The concentric striae are studded 

 with elongated nodes or tubercles, which are thus arranged in parallel bands, more or 

 less contiguous, according to the" distance of the concentric striae. 



The elongate tubercles may perhaps more properly be regarded as interrupted 

 radiating striae, which, in the perfect condition of the shell, have doubtless extended in 

 slender spines or setae. (They are termed by Mr. Conrad short longitudinal striae.) 



The area is strongly striated vertically." 



Remarks — This is a rare species in the Mineola faunas of Missouri and most of the 

 specimens are imperfectly preserved. On one specimen the fine undulating lamellose 

 striae are well preserved and two specimens show the radiating lines which represent the 

 elongated nodes or tubercles. 



Occurrence — Mineola of Montgomery and Warren Counties. 



Genus Martinia McCoy 



Martinia halli n. sp. 

 Plate 16, figures 6-8 



Description — Shell small, subcircular in outline, cardinal extremities rounded. 

 The dimensions of two nearly perfect specimens are: Length of pedicle valve 7.7 mm., 

 6 mm.; width 8 mm., 6.7 mm.; thickness 6 mm., 4 mm.; length of brachial valve, 7 

 mm., 5.4 mm. 



Pedicle valve strongly and uniformly convex, the greatest convexity a little in front 

 of the hinge line; umbo prominent and projecting beyond the hinge line; curve to the 

 beak a little stronger than that toward the front of the shell ; a faint indication of a mesial 

 sinus on the anterior half of the shell. Cardinal area small, strongly arched, the lateral 

 margins rounded; delthyrium small. 



Brachial valve about two-thirds as convex as the pedicle, the greatest convexity 

 near the hinge line, the surface sloping almost uniformly in all directions. No indi- 

 cation of a mesial fold. Beak small, cardinal area very narrow. 



Both valves seem to be smooth. The description is based on six specimens, three of 

 which are excellently preserved and show no markings. 



Occurrence — Callaway limestone of Moniteau County. The species is named for 

 Mr. Roy H. Hall, who mapped the Devonian of Moniteau County and collected the 

 first specimens of the species. 



Family Suessiidae 

 Genus Cyrtina Davidson 



Cyrtina hamiltonensis (Hall) 



Plate 19, figures 5-8 



1857. Cyrtia hamiltonensis Hall, Tenth Rep. N. Y. State Cab. Nat. Hist., p. 166. 

 1861. Cyrtia Hamiltonensis Billings, Canadian Jour., VI, p. 262, figs. 80-82. 

 1863. Cyrtina Hamiltonensis Billings, Geol. Canada, p. 384, fig. 415. 





