* 
384 Say on Shelis, dpe. 
but on the thoracic plate of Limulus 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 alyeoles 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. 7 
Genus Favosites, Lam. 
Coral lapideous, simple, of a variable form, composed of 
parallel prismatic and fasciculated tubes; tubes contiguous, pen- 
tagonal, or hexagonal, more or less angular, rarely articu- 
lated, 
Species. 
G. striata, more or less turbinate ; paries of the alveoles 
longitudinally. striated within, and fenestrate with minute 0- 
euli; alveoles with very numerous septe. (Cabinet Acad. Nat. 
Sciences ; and Peale’s Musewm—common.) 
Found fossil in various parts of the United States, at the 
falls.of the Ohio; Gennesee, New-York ; Pittsburgh and Wilks- 
barre, Pennsylvania; Missouri, &¢. &c. but not yet in the 
alluvial deposit of N ew-Jersey, : 
The tubes are generally, partially, or entirely filled with 
silicious. matter, sometimes so completely, as to resemble — 
