548 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
No specimens were found in the collections from the New England 
coast made by the U. S. Fish Commission, and it is evidently very 
rare there. 
Subfamily Tethyinae Hartmeyer, 1908. 
Characters approximately those given for the family. Comprises 
simple ascidians only, which never reproduce by budding. 
Genus Tethyum Bohadsch, 1761. 
[= Styejla auct. plur.]. 
Apertures both four-lobed. 
Branchial sac regularly with four folds on each side, but one or more 
may be rudimentary or wanting, or a rudimentary fifth fold may 
occur (not in any New England species). 
Tentacles simple. 
Dorsal lamina usually plain, sometimes slightly toothed. 
Ovaries phial-shaped or tubular with one end closed; one or more 
on each side of the body. The small testes generally arranged along 
the border of the ovary, either close to it, forming a compact gonad, 
or separated a little way from it. 
This genus, which is one of the largest and most widely distributed 
genera of ascidians, is second only to Caesira in the number of species 
represented in the New England region. Seven from this region are 
here described in addition to one from the North Carolina coast. 
Key to the Species. 
1 . Gonads each consisting of a crooked tubular ovary and a varying number 
of small testes, the latter attached to the mantle at a httle distance from the 
margin of the ovary. 
A. Gonads usually one on each side. 
Body surface coarsely wrinkled, usually a pointed projection between 
the orifices rusticum. 
Body surface with many very minute rounded semitransparent tuber- 
cles, body usually dorso-ventrally flattened coriaceum. 
B. Gonads usually two on each side. 
Testes chiefly grouped about the ventral ends of the ovaries. Inhabits 
moderately deep water atlanticum. 
Testes of irregular, often more or less branching form, arranged along 
each side of the ovaries as well as about their ventral ends. In- 
habits shallow water partitum. 
2. Gonads each consisting of a flask-shaped or elongated ovary overlying 
or closely bordered by a number of small pyriform or lobed testes, the 
whole forming a compact mass. 
