360 FUNAFUTI ATOLL. 



There are eight pieces, evidently detached from one large speci- 

 men ; the largest is 12 cm. in length, and 7 cm, broad at the outer 

 extremity. 



Reefs in the lagoon. 



MADREPORA IMPRESSA, sp. nov. 

 One example obtained in the lagoon. 



Corallum consisting of a subreniform plate, spreading out from 

 a lateral attachment ; the plate is 30 cm. long, from 14 to 20 cm. 

 broad, 11*5 cm. thick at the point of attachment, from thence 

 thinning ont gradually to 1 cm. or less at the margin. 



The living layer, as in other species of the subgenus Isopora, is 

 about 1 cm. in thickness. The under surface is smooth and desti- 

 tute of corallites. The basal epitheca is marked by a series of 

 concentric ridges, indicating the lines of growth. 



Upper surface very uneven, covered with low, irregularly 

 rounded elevations, 1 cm. in diameter, 5 mm. high, and usually 

 about 7 mm. apart, The intervening depressions vary in shape 

 from subcircular to elongate, the latter form occurring near the 

 margins, where the elevations are more or less connected by 

 narrow ridges. Besides the numerous small prominences, there 

 are six or seven larger ones from 2 to 3 cm. high and 3*5 cm. in 

 diameter. 



A few obtuse, compressed, or subquadrate branches are present 

 near the margin, the largest is 3 cm. in height and 1'5 cm. in 

 diameter. 



Axial corallites numerous, situated in groups on the elevations, 

 from 1'5 to 2 mm. in diameter; aperture circular, small, rarely 

 exceeding 0-7 mm., generally between 0-5 and 0-6 mm. in diameter; 

 walls 0'6 to 0'7 mm. in thickness, often confluent to the summits, 

 which are plane or but little rounded. 



Septa in two cycles, the directives seldom more than O'l mm. 

 broad at the margin and about 0'15 at the base, the remaining 

 primaries are very narrow, the secondaries barely distinguishable. 



Radial corallites crowded, frequently confluent, subimmersed, 

 nariform, tubo-nariform, or tubular ; inner part of wall occasion- 

 ally incomplete. Apices rounded, but generally thin and denti- 

 culate at the margin; diameter about 1'5 mm., length up to 2'5 

 mm. 



The second cycle of septa either absent or rudimentary, primaries 

 similar to those of the axial corallites. 



Oorallite walls densely covered with compressed denticulate 

 echinulations, 0'15 mm. high and about O'l mm. apart. 



