26G 
THE VOYAGE OF H.M.S. CHALLENGER. 
The Test is firm and cartilaginous. It is of a grey colour, and is semi-transparent. 
The matrix is clear and structureless. It contains minute inconspicuous test cells, and a 
considerable number of large bladder ceUs, but no calcareous spicules are present. 
Locality. — Off Bermuda, shallow water. 
This is a colony of compact rounded form which was dredged off Bermuda in shallow 
water (PI. XXXIV. fig. 6). It is unlike any other species in the collection, and is, I think, 
distinct from any known species of Compound Ascidian; but unfortunately, on account 
of the condition of the Ascidiozooids in the single colony at my disposal, it is impossible 
to give a complete specific description, or even to refer the specimen to its proper 
genus with certainty. All the Ascidiozooids are apparently in a decomposed condition ; 
they are found on examination to be merely rounded or elongated masses of granular 
debris. Probably the colony was dead and in a decaying condition when collected. 
It is simply from the general appearance, and not from any structural feature, that I 
place this specimen in the Didemnidse, but it is quite possible that it may really belong to 
the Polyclinidse. If, however, it is correctly placed in the present family, then, on 
account of its massive form (PI. XXXIV. fig. 6), there can be little doubt that its genus 
is Didemnum or Didemnoides. As the former is the commoner and more widely 
distributed genus, I have provisionally placed the species there. 
The test, as is usual in Compound Ascidians, even when the Ascidiozooids are dead, 
is in good condition, but no spicules are present. This, although unusual in the 
Didemnidae, is not an unknown condition, as von Drasche’s two species, Didemnum 
inarmatum and Didemnum tortuosum} have no spicules in the test. 
The bladder cells are large and fairly numerous (PI. XXXIV. fig. 7, hl.\ They are 
of the usual ellipsoidal form, with distinct laterally placed nuclei. The test cells are of 
various shapes, but are all of small size (PL XXXIV. fig. 7, t.c.). 
L&ptoclinum, Milne-Edwards. 
Leptoclinum, Milne-Edwards, Observations sur les Ascidies Compos^es, 1841. 
Leptoclinum, Giard, Eecbercbes sur les Synascidies, &c., Archives d. Zool. exper., t. i. p. 651, 
1872. 
Leptoclinum, Della Valle, Contribuzioni, &c., 1877. 
Leptoclinum, von Drascbe, Die Synascidien, &c., p. 33, 1883 (as a subgenus). 
Colony forming a thin incrusting layer, rarely thick and massive. 
Ascidiozooids with the atrial aperture on or near the anterior end of the body, and 
provided with a long languet. 
Test very hard and firm, densely crowded with calcareous spicules. 
Branchial Sac usually with four rows of stigmata. 
^ Die Synascidien der Bucbt von Eovigno, p. 32, 1883. 
