234 A. E. VerrUl — Corals of the Genus Acropora. 



nal branches are mostly only 25 to 50 mm long, and taper rapidly. 

 They stand at various angles ; some are almost squarrose. 



Most specimens grow taller (np to 2 feet high=600 mm ) and branch 

 more arborescently, with longer and more distant branches, variable 

 in size. This was the case with Dana's Singapore type. 



But the characters of the corallites are generally pretty constant 

 in all. The axial corallites are nearly always large and swollen, with 

 thick, porous walls; their diameter is commonly 4 to 5""", but varies 

 from 3 to 6 mm on a single specimen ; their calicles are about 2 mna 

 broad ; the naked, exsert portion may be 2-3 mm in length. 



The radial corallites are .various in size and form on one branch. 

 The larger ones, in typical nobilis, are dimidiate-cylindrical or spout- 

 like, scarcely at all compressed, with the lower lip thick and 

 rounded, rather long, porous, often slightly expanded, frequently a 

 little incurved, but distally on the branches more spreading and 

 often a little excurved, though the greater number are nearly straight 

 on the outer side; they stand at angles of 50° to 90°, but more gen- 

 erally at 60° to 70°. The inner lip is usually short and thin. The 

 larger ones are usually about 2-2. 5 mm broad and 2 to 4""" long. 



Their septa are very distinctly stellate, with six rather wide 

 primary septa, the directives wider, and six narrow ones of the second 

 cycle. The axial corallites have 12 distinct septa, rarely 24. 



The walls of the axial and radial corallites are strongly costulate, 

 with pores between the costulse ; the lower lip of the radial coral- 

 lites is fenestrate-porous distally. The coenenchyma is very porous 

 and pitted, and roughly granulated. 



Between the larger radial corallites there are many small labellate 

 or dimidiate ones, with the outer lip either long or short, straight or 

 incurved, and also a few that are nearly or quite immersed. 



Var. secunda Ver., 1864. 



Madrepora secunda Dana, op. cit., p. 487, pi. xl, tig. 4. 



One of Dana's types of this form, in the Yale Museum, forms a 

 loosely, arborescently branched clump, about 10 inches high (250 mi "), 

 with the main branches rather long and divergent, about 1 5 to 1 8 mm 

 in diameter, branching freely distally, with evenly tapered branches. 



In its form and mode of branching it does not differ from many 

 typical specimens of nobilis, but the main blanches are more slender 

 than usual. 



The terminal or axial corallites are thick and swollen, porous, and 

 costulate, formed exactly as in nobilis, though they average rather 



