•102 PALAEONTOLOGY OF NEW-YORK. 



The figures 1-7 of Plate xlvii illustrate the general features of this species. 



Oeological formation and localUi/. In the Iluiniltou group at Delphi, New-York. 

 A sin<»-lc specimen from the Chemung group Is undistiuguishablo irom those of 

 the lliuuilton group. 



Atliyi'is angelica. 



PLATE XLVII. 



JilhyrU angelica : Hall, Fourteenth Report on the Stat« Cabinet, p. 99. 1861. 



Shell ovoid, gibbous, transverse or elongate ; proportions of length and 

 width variable, the prevailing form longer than wide ; deeply sinuate, 

 with the beak very prominent ; hinge-line short. 



Ventral valve gibbous, most convex above the middle ; mesial sinus 

 usually extending nearly to the beak, becoming abruptly and deeply 

 depressed below the middle, and much expanded towards the front of 

 the shell ; lateral portions of the valve gibbous, and abruptly curving 

 towards the margins : beak much elevated and curved over the umbo 

 of the dorsal valve. 



Dorsal valve much shorter than the opposite, gibbous, transverse or as 

 long as wide ; the mesial fold usually not conspicuous above the lower 

 third of the valve : in the upper part the surface is a little more gibbous, 

 and the strife along this part are more straight or a little curved back- 

 wards, indicating the form during the successive stages of growth. 



Surface marked by regular equidistant imbricating lamellas or lamelli- 

 form stria3, the edges of which in perfect specimens are projecting 

 and slightly crenulate. These lamella3 are marked by short inter- 

 rupted radiating striaj, as shown in figure 20. 

 The interior of the ventral valve shows a semicircular perforation at 



the apex, opening on the lower side to a triangular fissure. The teeth are 



strong, and continued in plates to the base of the rostral cavity. 



The adductor imprints are strongly marked just below the rostral cavity, 



and the divaricator imprints occupy an ovate space below and on each 



side. Surface of cast, adjacent to the muscular imprints, strongly 



papillose. 



