T2 Memoirs of the Indian Museum. [More Vale 
processes of the test are in H. psammatodes least numerous on the ventral side, while in 
our species these processes are best developed at the posterior end, evidently corres- 
ponding to the ventral side of the Malayan species. 
The musculature of the mantle exhibits, roughly speaking, the same type of 
arrangement in both species. There are but few muscle bands on the trunk proper, 
while on the siphons they are pretty well developed. The strongest muscle bands are 
found in both species along the margin of the branchial aperture and inside the 
tentacle-like lobes surrounding it. 
The tentacles show a very striking difference in the two species. In H. psamma- 
todes there are more than a hundred tentacles having the form of short finger-like 
filaments. As stated above, our species has no tentacles at all. 
The branchial sac, which is the most characteristic feature of the genus, exhibits 
a wonderful conformity in the two species. In both forms it is narrow, and its walls 
are perfectly intact, there being no stigmata perforating them. Between the pharyn- 
geal portion of the alimentary canal and the oesophagus there is no visible constric- 
tion, so that these two regions cannot be sharply defined. 
The course of the alimentary canal is very different in the two species. In 
H. psammatodes it is very short and wide, and runs almost in a straight line to the 
anus at the hind end of the trunk, there being no stomach and no intestinal loop, a 
condition not found in any other known Ascidian. The liver, which is a conspicu- 
ous organ in our species, was not observed in H. psammatodes. 
The gonads show partly a close agreement and partly a remarkable discrepancy 
in the two species. Both have the testes and ovaries developed one on each side, 
and the gonoducts are all separate. The testis is roughly oval in outline, while the 
ovary is elongated and bent in knee-like fashion. But in H. psammatodes each geni- 
tal gland is provided with a large bladder-like sac with thin membranous walls, and 
differs in this respect markedly from the gonads of all other Ascidians. In the pres- 
ent species nothing comparable to these sacs could be observed. 
The excretory organ is not mentioned in Sluiter’ s description of his species. In 
H. indicus, on the other hand, there is a large globular renal sac containing brown 
concretions, exactly like that of a typical Molgula. 
As seen from the above comparison, the two species, while agreeing in many im- 
portant points of structure, still exhibit so great a difference that it would seem 
almost necessary to regard them as the types of two different genera. When we 
consider, however, that they agree in a most striking manner just in those points 
which separate them so widely from all other Ascidians, and further that only a single 
specimen of H. psammatodes could be examined, which of course made the investiga- 
tion of the internal anatomy somewhat difficult, it is thought best, at least for the 
present, to unite the two forms under one generic title and amend the diagnosis of the 
genus Hexacrobylus accordingly. Under these considerations I have decided to name 
our species Hexacrobylus indicus. 
The only other simple Ascidian hitherto known which shows any close affinity 
to the genus Hexacrobylus is the curious deep-sea form Oligotrema psammites, collec- 
