EASTERN COAST OF THE UNITED STATES. 



39 



of and above the cells in all the genera examined, and, on contraction, of sinking back into 

 them. The tentacles are slender and well developed. 



This group embraces three divisions of Milne-Edwards, which may be regarded as sub- 

 families, viz : I. Astrwacew, including those genera that form massive corals by the inti- 

 mate union of the individuals. These bud near or within the disk or from the membrane 

 connecting contiguous polyps ; II. Cladocoracece, comprising those that bud laterally and in 

 which the polyps are united only at the base, forming branching or csespitose clumps ; III. 

 Astrangiacece, in which the polyps bud from the base, from basal expansions or, more rare- 

 ly, from the sides, forming, mostly, low incrusting corals. These last two groups ought 

 perhaps to be united, since the separation between even the typical genera, Cladocora and 

 Astrangia, is not very clear, the former, while young, budding from basal, creeping stolons, 

 and some species of the latter rising when old into incipient branches and increasing thus 

 by lateral, or even marginal, buds. 



The last of these subdivisions is the only one found within our limits. 



Genus Astrangia M.-Edw. and Haime. 

 Astrangia M.-Edw. and Haime, Comptes-rendus, xxvii. p. 496 (1848). 



Corallum incrusting, the corallites arising from an expansion of the base of the parent, 

 and sometimes from the walls or margin, forming either clustered groups or aggregated, 

 astrea-like masses, sometimes with rising branches. Walls naked and costate. The cells 

 are circular except where crowded, deep, with numerous subequal septa, which are all den- 

 tate, those of the last cycle curved ; columella papillose ; dissepiments few. The polyps 

 when expanded are subtransparent, and rise to a considerable distance above the cells. 

 The tentacles are long, slender, covered by minute white warts, consisting of lasso-cells, 

 and have a knob at the tip. 



Astrangia astrseiformis M.-Edw. and Haime. 

 Astrangia astraiformis M.-Edw. and Haime, Ann. des Sci. Nat., 3d ser. xii. p. 181 (1850). 



Corallum composed of closely aggregated corallites, united nearly to their summit, spread- 

 ing over and incrusting the surface of shells, and, by continued growth, forming astrea- 

 like masses of considerable thickness, which often rise into numerous short irregular 

 branches. In these, besides the marginal buds that arise from the basal expansion, many 

 originate from the sides of the parent polyps and some even from the margin of the disk. 

 The cells are widely open, deep, and narrow at the bottom. Columella well developed, 

 papillose, the papilla? confounded with the inner teeth of the septa. Septa much narrowed 

 at the top, in three complete cycles, often with some of a fourth ; those of the third 

 cycle are well developed, and curve towards those of the preceding one, uniting with 

 them interiorly; all of them have the sides granulated and the edges sharply dentate. 

 Costaa w r ell marked near the margin. Thickness or height above the base, often two 

 inches; diameter of the cells about .18 inch. (Coll. Mus. Comp. Zool.) 



Charleston, S. C. (L. Agassiz) ; Beaufort, N. C. (A. S. Bickmore). 



This species often incrusts shells that are inhabited by hermit crabs. 



