2 Memoirs of the Indian Museum. [MOL Wie 
to the internal anatomy of the animal. One specimen was carefully dissected and 
two others, removed from the test, were stained with borax carmine and cut 
into sections. Pl. III, fig. 2, is a reconstruction from such sections and represents, 
satisfactorily I hope, the relations of the internal organs of this very curious 
Ascidian. 
The new genus Monobotryllus is interesting inasmuch as it represents a connect- 
ing link between the two families, the Styelidae and the Polystyelidae. Although 
itself a simple Ascidian, it is most closely allied, not to any of the simple forms, but 
to some members of holosomatous compound Ascidians. In the shape and position 
of the branchial sac and alimentary canal it very much resembles the genus Botryl- 
lus or Botrylloides, while in the arrangement of the gonads, which are hermaphrodite 
polycarps, it is so exactly like the genus Michaelsenia among the Polystyelidae that 
nobody would hesitate placing it in that genus, were the individuals found imbedded, 
in a common test. This furnishes another instance showing that the division of the 
Ascidians into simple and compound forms is simply a matter of convenience. 
The occurrence of a representative of the genus Megalocercus in the Indian Seas 
is of much interest zoo-geographically. This genus has hitherto been known only 
from three specimens procured from a considerable depth (600 and goo meters) near 
Ischia and Capri in the Mediterranean. 
Two specimens of simple Ascidians, belonging to widely different species, Poly- 
carpa annandalei, n. sp., and Ascidia willeyi, n. sp., harboured each in the branchial 
sac a pair of macrurous crustaceans, which, judging from their size, must have en- 
tered the body of the host as larvae and grown up there to maturity. Although a 
number of crustaceans may frequently be found in the branchial sac or atrial 
cavity of Ascidians they are almost always amphipods or copepods; commensal 
macrurans living in pairs, as those found in the interior of the siliceous sponge 
Euplectella, have, so far as I am aware, never been recorded from Ascidians. 
Before proceeding to the description of the species I wish to express my cordial 
thanks to Dr. N. Annandale, Superintendent of the Indian Museum, Calcutta, for 
having given me the opportunity of studying a material including so many interest- 
ing forms. 
ASCIDIAE SIMPLICES. 
Fam. MOLGULIDAE. 
This family is represented in the collection by three species. Two of these belong 
to the genus Molgula (Caesiva) and, though both of them are new to science, do not 
exhibit any striking characters. The third is a very remarkable form apparently 
belonging to the genus Hexacrobylus, Sluiter, which has hitherto been considered as 
the type of a separate order, the Aspiraculata, on account of the total absence of 
stigmata in the branchial sac. After a careful study of the internal anatomy, how- 
ever, I came to the conclusion that it is more natural and convenient to place it, 
notwithstanding its most aberrent characters, in the family Molgulidae. A pre- 
liminary note on this animal giving the reasons for regarding it as a highly modified 
