8 PROCEEDINGS OF THE ACADEMY OP 



The external characters of this shell resemble those of Spirif era simplex, Phil. 

 (Pal. Foss. p. 71, pi. xxix. fig. 124, and pi. lx. fig. 124), but the hinge-line is 

 more elongate. 



This species, so far as is certainly known, is restricted to the base of the 

 Burlington limestone. 



Syringothyris Halli, n. sp Shell of medium size, transversely elongate, 

 widest aloDg the hinge-line ; greatest depth of the two valves equalling or ex- 

 ceeding the greatest length. Ventral valve with a deep, defined sinus; beak 

 very elevated : surface sloping thence with but little convexity, to all parts of 

 the margin, being sometimes even concave between the apex and the cardinal 

 extremities ; area large, triangular, transversely striate, flat or slightly arched, 

 with a more marked incurvation just beneath the beak ; perforated by a narrow, 

 or moderately wide, triangular fissure, which is grooved along its lateral bor- 

 ders as if for the reception of a deltidium ; dental plates rather short in a va- 

 riety, very short diverging at an angle of G6 ; mesial septum a low ridge ex- 

 tending two-fifths the length of the valve ; line of divaricator scars extending 

 with a curve from inner end of dental plates to inner end of mesial septum. 

 Dorsal valve moderately ventricose, with a convex surface, and abrupt well- 

 defined mesial elevation, and a small beak which overhangs the base of the 

 fissure in the area of the opposite valve, the area being scarcely perceptible 

 in the dorsal valve. Surface ornamented by 12 to 16 rounded ribs on each 

 side of the mesial fold and sinus, becoming obsolete toward the lateral angles. 

 Mesial fold and sinus destitute of ribs. The whole surface is further marked 

 by faint, delicate lines of growth. 



Length of hinge-line 1-32 (100) ; depth from beak of ventral valve to most 

 prominent pointof dorsal which is nearly at right angles to the plane of the 

 valves *70 (53) ; distauce from hinge-line to middle of anterior margin 

 54 (41) ; elevation of (ventral) area -48 (36) ; width of fissure at base 

 28 (21). 



Ranges through the yellow sandstones. In bed No. 1 is a variety with some- 

 what convex area, very narrow fissure and very short dental plates. The species 

 occurs also at Clarksville, Mo., where the beak of the ventral valve is bent 

 somewhat to the left (this beak being uppermost) in the style of a Streptorhyn- 

 chus producing a curvature of the mesial sinus and the fissure ; and is further 

 peculiarly marked by several distinct lamellar wrinkles of growth. 



Named in honor of Prof. James Kail, the eminent Palaeontologist of Albany, 



N. Y. 



AVICULA, (Klein,) Bruguiere. 



Avicula Whitei, n. sp. Shell large, transverse, exceedingly oblique, with 

 neariv terminal beaks. Hinge-line more than three times the greatest dorso- 

 ventral dimension. Anterior ear pouched, not distinctly divided from the body 

 of the shell. Left valve ventricose; umbonal ridge somewhat arcuate, or 

 nearly straight, forming an angle of about 20, with the hinge-line ; slope 

 thence to the ventral margin very rapid to the dorsal side rather gradual and 

 symmetrical to the very hinge-line the posterior wing not being divided from 

 The body of the shell. Ventral margin, in the middle rather straight and near- 

 ly parallel with the dorsal ; posterior margin sigmoidal by a deep, or rather 

 shallow sinus, isolating the posterior end of the cartilage plate from the body 

 of the shell; posterior wing triangular, exceeding the shell. External surface 

 marked by numerous fine, irregular stria? of growth. Right valve much less 

 ventricose, marked on the body and anterior slope by numerous sharp, regular 

 raised concentric strire which become very faint posteriorly. Cardinal line in 

 each valve with a long, slender, bifid lateral tooth behind the beak. 



Length of dorsal side 2-13 (100) ; greatest dorso-ventral dimension -70 (33) : 

 depth of left valve -22 (10). 



Avicula acanthoptera, Hall, (Geol. Rep. 4th Dist. N. Y., p. 263). Shell 



[Jan. 



