VAN NAME: SIMPLE ASCIDIANS. 
495 
ever, a considerably larger size. Test of moderate thickness and firm 
consistency, very transparent, allowing much of the internal structure 
to be seen. 
Musculature of mantle slight, consisting of very slender, rather 
widely separated bands, forming on parts of the body a fairly regular 
network with more or less rectangular meshes. 
Tentacles of several sizes quite regu- 
larly arranged. Even the large ones 
have comparatively few branches and 
are not more than twice pinnate. Tips 
of branchlets blunt and slightly swollen. 
Dorsal lamina plain-edged. 
Dorsal tubercle C-shaped, the horns 
decidedly incurved, opening directed to 
right rear. 
Branchial sac with five moderately 
prominent folds on each side. Appar- 
ently but five principal transverse 
vessels, but more or less complete 
intermediate ones may develop in some 
of the intervals. Internal longitudinal 
vessels stout and confined to the folds: 
three on the first four folds, two on the 
fifth (most ventral) fold. One or two 
infundibula on the summit of each fold 
in each space marked oft' by the prin- 
cipal transverse vessels. Also a series of spirally arranged stigmata 
representing rudimentary infundibula between the median dorsal 
vessel and the first fold, and some more or less irregularly disposed 
ones ventral to the last fold. 
Stigmata mostly wide and long, not very numerous; arranged in 
fairly distinct double spirals on the infundibula. Free ends of the 
spirals mostly come out of the spirals near the odd-numbered princi- 
pal transverse vessels. 
But two small specimens of this species are in the collection. They 
were obtained at Murray Bay, Gulf of Saint Lawrence, by Dr. J. W. 
Dawson. Stimpson had the species from George's Bank, 30 fathoms. 
Professor Verrill informed the writer that he had never found it in all 
the extensive collecting that he had done, and the species is evidently 
Text-flg. 12. — • Caesira crystal- 
Una (Moller). (Outline of test 
shown.) X 5.2. 
