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PALAEONTOLOGY OF NEW-YORK. 
Mliyiichoiielia speciosa. 
Plate CHI A. Fig. 1-6. 
lihynclwnella speciosa : Hall, Regents’ Report for 1856, p. 81; Palaeozoic Fossils, 1857, p. 41. 
Shell longitudinally ovoid, vertically flattened on the sides, higher than 
wide, abruptly rounded or subtruncate in front; sides nearly parallel: 
no sinus in either valve. Dorsal valve extremely elevated, abruptly 
inflected on each side towards the opposite valve : beak incurved ; 
cardinal margin on each side of the beak profoundly sinuate, for the 
reception of the rounded auriculate processes of the opposite valve ; 
anterior and lateral margins uniting by sharp prominent interlocking 
serrations. Ventral valve depressed convex near the beak and flattened 
in the middle, forming a regular elliptical arch from beak to front, and 
abruptly inflected at the sides so as to form distinct angles along the 
lateral margins, the entire front of the valve forming a broad truncated 
projection : beak somewhat obtuse, incurved. 
Surface marked by strongly elevated, rounded or very obtusely subangu- 
lar plications, each of which, on the front and sides of the shell, has a 
fine depressed line along the centre, crossed by fine regular concentric 
zigzag lines of growth. 
The interior of the ventral valve shows a very distinct oval muscular 
impression, in which the adductors are but faintly defined : the median 
division is very faint. The dental processes are small and slender, and 
placed just within the edge of a prominent auricular extension of the 
valve which fills the sinus of the opposite one. The margins of the valve, 
from the dental process to the beginning of the anterior portion, are in¬ 
flected at right angles to the transverse axis or plane of the valve. The 
marks of the plications extend into the interior nearly as far as the 
muscular impression. 
The interior of the dorsal valve shows an elevated median septum, 
