NIAGARA GROtrr. 



281 



643. 57. ATRYPA CORALLIFERA (»j. 5;).)- 



PL. LVII. Fig.ba-t. 



Rhomboidal or siibtriangular, the base being often nearly straight, more or less convex, anil 

 sometimes gibbous ; valves nearly equal, a deep sinus in the dorsal and a corresponding eleva- 

 tion in the ventral valve ; beak of the dorsal valve closely incurved over the A'entral valve ; 

 surface covered by a finely reticulated membrane-like envelope, having the appearance of a 

 flustroid coral ; cast punctate, the ventral valve with a deep slit down the centre of the mesial 

 fold, while the dorsal valve shows the cast of a small rostral cavity, without subdivisions or 

 lamina on either side. 



This species is readily recognized by its peculiar surface marking, which appears like one of 

 the finely reticulated corals of the Flustra tribe. This covering, however, is the outer portion, 

 or entire shell ; for when removed, the characteristic features of the cast are visible, and the 

 whole surface has a finely punctate character. In some specimens the shell has become much 

 thickened, imbricating lines of growth are more or less distinctly visible, and the intervals 

 between the reticulating spaces are punctate, in similar manner to the corals of the Genus 

 Callopora. a slight exfoliation of the surfaces, however, in specimens having this character, 

 and in others, shows a simple pimctate surface with fine concentric lines. 



Fig. 5 a. A young individual of this species. 



Fig. 5 b. A larger specimen of this species. 



Fig. 5 c, d. Ventral and dorsal views of a specimen of the ordinary or prevailing size. 



Fig. 5 e, f. g, k. Front views of di-iierent specimens, one of which is compressed, and the others 



retain their natural proportions. 

 Fig. 5 i, k. Profile views of two individuals, one of which is very gibbous. 

 Fig. 5 I, m. Cardinal views of other individuals. 

 Fig. 5 n, o. Casts of the dorsal valves of two individuals, the last one larger and proportionally 



more extended laterally than any other specimen observed. 

 Fig. 5 p. Cast of the ventral valve. 



Fig. 5 r. An enlarger.ient of the surface, presenting its ordinary character. 

 Fig. 5 s. An enlargement of the surface, where tlie shell is thickened, and the spaces between 



the reticulate openings is punctate. 

 Fig. 5 t. An enlargement of the surface of the cast of this species, showing the punctate character. 



Position and locality. This species has been found in the shale at Lockport, and at Ro- 

 chester. 



[Fal^eontology — Vol. ii.] 36 



