54 
Proceedings of the Royal Society 
Microcosmus, Heller. 
This genus is distinguished from Cynthia, according to Heller,* 
by the possession of a plain-edged dorsal lamina and a narrow 
intestinal loop ; while in all species of Cynthia proper the dorsal 
lamina is denticulated on the free margin, and the intestine forms 
a wide loop. 
It is undoubtedly convenient to separate the two groups of 
species, and they form very natural sections of Cynthia; but 
whether the denticulation of the dorsal lamina, and the amount of 
curvature in the intestine are sufficient characters for the formation 
of a separate genus is, I think, rather doubtful. 
Microcosmus. 
Branchial sac having Branchial sac having 
six folds on each seven folds on each 
side. side. 
M. helleri. 
Surface of test very Surface of test 
rough and irregular. not rough. 
M. polymorphus. M. propinquus. 
Microcosmus helleri, n.sp. 
External appearance. — Shape longish, elliptical, with a projection 
at the anterior end; posterior end broad and rounded. Attached by 
a small area at the posterior end of the ventral edge. Branchial 
aperture at the anterior end of the dorsal edge, terminal, on a large 
projection, directed anteriorly. Atrial aperture on the dorsal edge, 
two-thirds of the way down, on a hemispherical projection, not 
so prominent as the branchial aperture, directed dorsally and pos- 
teriorly. Surface wrinkled and rough, but not covered with ex- 
crescences ; branchial and atrial projections much corrugated and 
thickened; a few zoophytes, polyzoa, &c., adhering, especially on 
* Heller, Untersuchungen uber die Tunicaten des Adriatischen und Mittel- 
meeres, iii. Abth., Wien, 1877, p. 3. 
