TRIBE III. MADREPORACEA. 433 



an even top clump (cespitose) ; spreading each way from a central 

 pedicel, and concave above (vasiform, or vase shape) ; spreading hori- 

 zontally or obliquely, and coalescing into a solid plate, without branch- 

 lets above (foliate}. A few species grow in erect plates clustered on a 

 common base, often incrusting, without any apical polyp, and these 

 form the transition to the genus Manopora. 



2. The size of the branches and branchlets : in adult specimens this 

 character admits of but little variation ; the size of the branchlets is 

 quite uniform in the same species. 



3. The frequency of branching: which determines whether the 

 branchlets are short, or long and tapering, crowded or few (confertim 

 out laxe ramosa}. 



4. The angle of branching : when this angle is small, the branches 

 and branchlets are closely ascending (stride ramosa) ; when as great 

 as 60, the usual angle, the clumps are quite open ramose (late 

 ramosa) ; when near 90 or reversed, they are divaricate. 



5. The character of the branches and branchlets: whether terete or 

 not, straight or curved, simple or proliferous, evenly or unevenly 

 covered with calicles, coalescent or not, as well as their size and posi- 

 tion as alluded to above. 



6. The form and position of the calicles, and the character of their 

 exterior surface, whether harsh and striate, or appearing smooth, and 

 either very fine striate or simply minute granulous, under the micro- 

 scope. 



7. When the branches coalesce, as they sometimes do, into a solid 

 plate, rudiments of the constituent branches or branchlets may gene- 

 rally be detected at the margin, and. as in other cases, the size of these 

 free branchlets is an important distinctive character. 



In describing the species, I have generally followed Ehrenberg, in 

 giving the definite dimensions of the calicles and branches, having 

 ascertained, by much study, the advantage to be derived in deter- 

 mining species, from a knowledge of the actual limits of variation in 

 this respect. 



The cespitose species appear to vary in shape somewhat according 

 to the depth at which they grow. In those near the surface, the 

 branches spread more nearly horizontally, and are consequently more 

 crowded and more completely coalescent; while those at greater 

 depths have a more ascending mode of growth, and the less coale- 

 scent branches appear longer and more subdivided. In the one case, 

 the clump is nearly flat below, while in the other it is subturbi- 



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