VAN NAME: SIMPLE ASCIDIANS. 537 
Though regretting to differ from so experienced an observer as 
Professor Michaelsen, the writer beheves that Pyura pedenicola 
Michaelsen, 1908b, should be included among the synonyms of this 
species. P. pedenicola was described from two small shrunken and 
poorly preserved specimens from the Banks of Newfoundland, which 
were insufficient, as Professor Michaelsen himself says, to make the 
internal structure entirely clear. The writer has found just such 
spines on P. aurantium as are illustrated for P. pedenicola, and in 
stunted shrunken specimens of the former he has found the gonads 
apparently, if not actually, fused into an irregularly branching body 
such as Michaelsen illustrates, though most of the branches at least, 
have their own oviducts. The supplementary dorsal languets men- 
tioned as especially characteristic of the new species occur in P. 
aurantium, and no other sufficient distinctions between the two 
species appear to exist. 
Genus Microcosmus Heller, 1877. 
Differs from Pyura in having the dorsal lamina a continuous, usually 
plain-edged membrane, and usually in having the intestinal loop much 
narrower. Stigmata always elongated in a direction parallel to the 
body axis. 
Microcosmus nacreus, sp. nov. 
PI. 56, fig. 75-77; PI. 57, fig. 82; PI. 7.3, fig. 162; text-fig. 26. 
Body of unsymmetrically oval outline when seen from one side, 
the part between the widely separated apertures forming nearly a 
straight line. Apertures four-lobed, on short, stout, conical siphons, 
or when retracted, level with the surface. Body usually thick from 
side to side in the anterior and dorsal part, but it narrows to a thin 
wedge-like border in the posterior ventral region. 
Length of largest specimen 40 mm., depth 35 mm., width 19 mm. 
Siphons separated by 22 mm. at their ends. 
Test cartilaginous, thicker in the ventral region, its substance 
densely crowded with coarse sand grains. External surface of body 
even, but covered with coarse sand and small pebbles except imme- 
diately about the orifices. Inner surface rough with small papillae 
due to these sand grains, and provided with a thick nacreous lining. 
