126 Mr. 8. O. Ridley’s Contributions to the 
chief importance to specimens collected by Mr. V. de Robil- 
lard at Mauritius, all those given below as from this locality 
having been obtained from that collector. But while the 
former were chiefly remarkable for size and beauty, and only 
secondarily for their novelty in some cases, those now to be de- 
scribed include some of the greatest interest from the rarity 
and high systematic importance of the types to which they 
belong, and will be seen to throw important light on the dis- 
tribution of the genera of Alcyonaria in our present seas. I 
have added notes on two species not from Mauritius, the 
reasons for which will be’ seen by reference to the remarks 
on Echinomuricea coccinea and Hunicella pergamentacea. 
Fam. Primnoide. 
ACIS. 
Acis, Duchassaing de Fonbressin & Michelotti, Mém. Cor. Ant. p. 19. 
This genus has hitherto been known only from the West In- 
dies, whence the above-named authors described the only known 
species, A. guadalupensis (l.c. p. 20, Guadelupe) and nutans 
(Suppl. Mém. Cor. Ant. p. 109, Santa Cruz): the one has a 
prominent verruca, covered with numerous squamous spicules, 
while that of the latter is barely raised above the general sur- 
face ; the one appears to connect the genus with Primnoa, the 
other with Muricea. The occurrence, as will now be shown, 
of this otherwise West-Indian genus in the Indian Ocean, and 
in its western portion in particular, has a peculiar significance 
for the student of geology, as showing that a communication 
probably existed between these two areas at a period later than 
that at which the genus was differentiated from the main stem 
of the family; the distribution of Villogorgia (see Ann. & 
Mag. Nat. Hist. ser. 5, vol. ix. p. 187) and Melitodes (Meli- 
thea, Lamarck &c.), in both which cases a single species of an 
exclusively or almost exclusively Indo-Pacific genus repre- 
sents it inthe West-Indian area, appears to show the same 
fact. This group, from the wide range of its species, is 
especially fitted to illustrate a truth of this kind. 
Acts ortentalis, sp. n. 
Corallum branching approximately in one plane; branching 
dichotomous, with the addition of alternating pinne at different 
points ; branches given off at short intervals. Common stem 
very short. Stem and branches cylindrical, hardly diminish- 
ing appreciably in thickness from the base upwards; ends of 
