438 On Ascension-Island Zoology. 
that no Mediterranean species is represented in this collection ; 
and the “ereat Agulhas current” to which Dr. Gwyn 
Jeffreys has directed attention is not only an efficient, but 
also, so far as the problem is raised by the characters of the 
Kchinoderm-fauna, a sufficient cause for the presence of the 
same species on both sides of the southern peninsula of the 
Old World. 
It may be of interest to add that Salenia varispina and 
Echinus acutus have been taken in deep water off Ascension. 
MADREPORARIA. 
Platygyra ascensionis, sp. n. 
The specimen which I venture thus to designate is unfor- 
tunately but a portion of what was probably a globose colony. 
It is somewhat worn, the summits of many of the intercalicular 
walls being rather rubbed and the septa of many of the calicles 
considerably broken. Enough, however, remains of its cha- 
racters to leave little doubt as to what they originally were. 
The species is decidedly fissiparous. The calicles are poly- 
gonal, generally either pentagonal or hexagonal, generally 
rather longer than they are broad, especially when about to 
divide; greatest diameter from 3 millim. to 5 millim., least 
diameter from 2 to 3 millim., depth about 2 millim. The 
calicles are absolutely united by their walls, which are barely 
1 millim. thick at bottom of calicle, and end somewhat 
bluntly above, the septa being slightly indicated as low teeth 
on the summit of the wall. ‘There are no traces of dissepiments 
or traverses, and seldom of lateral union between the septa. 
Septa in three cycles, the rudimentary third cycle frequently 
wanting, generally about three primaries to a millimetre; 
the primaries project horizontally about 1°5 millim. from the 
wall, and then slope gradually to the columella, to which 
they are intimately united; secondaries only about half as 
wide as the primaries ; tertiaries, where present, mere ridges 
on the wall. Septa thin, but strongly roughened by lateral 
tubercles ; edges of primar ies decidedly dentate, those of infe- 
rior cycles slightly so. Columella distinct, normally spongy, 
but drawn out into a linear form in calicles about to divide. 
Tissue of walls and of the part subjacent to the calicles 
dense and non-cellular. 
This species is a very interesting one, as showing a marked 
divergence frem the ordinary type of the genus (Plat YY? a, 
Ehrb.,= Caloria+ Astroria, M.-Kdw. & Haime) to which 1 
have assigned it ; it appears to fall into the Aséroria division 
