384 •S'aiy on Shells, 4^c. 



but on the thoracic plate of Umulus polyphemus, having a con- 

 siderable space over which to extend themselves, the strata 

 are but few, not more than 2 or 3. I have seen the thoracic 

 plate of this animal so entirely covered by the Alveolite, as to 

 have the eyes and stemmata concealed so as to be perfectly 

 blind. When composed of a single layer only, it much resem- 

 bles a Flustra, or a Cellapore of which the convex surfaces have 

 been removed by attrition. The animal I have not yet exa- 

 mined. The alveoles or cells of a layer, are arranged in lines 

 of different degrees of curvature, obscurely radiating from dif- 

 ferent centres ; these lines are placed side by side, the alve- 

 oles alternating with each other throughout the layer in a 

 quincunx manner ; the thickness of the paries is somewhat 

 equal to one half of the conjugate diameter of the alveole, the 

 length of which, or thickness of the layer, is scarcely more 

 considerable ; but these proportions vary. 



The species to which it seems allied, are madreporacea and 

 incrustans. The former is fossil, and differs in being subra- 

 mose ; the latter forms but a single expansion. 



Genus Favosites, Lam. 



Coral lapideous, simple, of a variable form, composed of 

 parallel prismatic and fasciculated tubes ; tubes contiguous, 

 pentagonal, or hexagonal, more or less angular, rarely arti- 

 culated. 



Species. 



F. striata, more or less turbinate ; paries of the alveoles 

 longitudinally striated within, and fenestrate with minute os- 

 culi ; alveoles with very numerous septae. (Cabinet Acad. JVat. 

 Sciences ; and PeaWs Museum — common.) 



Found fossil in various parts of the United States, at the 

 falls of the Ohio ; Genessee, New- York ; Pittsburg and Wilks- 

 barre, Pennsylvania ; Missouri, &c. &c. but not yet in the 

 alluvial deposit of New-Jersey. 



The tubes are generally, partially, or entirely filled with 

 silicious matter, sometimes so completely so, as to resemble 



