VAN NAME: SIMPLE ASCIDIANS. 457 
closed sac in which concretions develop, is usually situated on the 
inner wall of the mantle on the right side of the body. 
Key to New England Genera of Caesiridae. 
Branchial sac with six or seven (rarely but five) curved longitudinal folds 
bearing several or many internal longitudinal vessels; reproductive organs 
on both sides of body ......... Caesira. 
Branchial sac without folds; seven stout widely separated internal longi- 
tudinal vessels on each side; reproductive organs on left side only. 
Bostrichobranch us . 
Genus Bostrichobranchus Traustedt, 1883. 
Branchial sac without folds. Five transverse and seven stout 
internal longitudinal vessels on each side. Wall of sac raised into 
internally projecting conical infundibula, numerous and irregular 
in distribution in old individuals, but showing more or less regularity 
in arrangement in young specimens. Two long stigmata form a per- 
fect double spiral on the wall of each infundibulum. 
Reproductive organs on the left side only, in and beside the intesti- 
nal loop. 
The genus is evidently derived from the genus Eugyra Alder and 
Hancock, 1870, from which it differs chiefly in the development of 
numerous secondary infundibula in the wall of the branchial sac, 
Eugyra having regularly but a single vertical row of large infundibula 
(or tW'O in the ventral region) in each of the spaces marked off by the 
transverse vessels. This is probably the most highly specialized 
genus of ascidians. It is known only from the American Atlantic 
coast, from the Gulf of Saint Lawrence to North Carolina, and though 
several species have been described, the writer after a study of many 
specimens has been unable to divide it into species distinguished by 
definite and constant characters. In this paper therefore its members 
will be treated provisionally as belonging to a single variable species. 
The related genus Eugyra Alder and Hancock, 1870, has' not been 
recorded from the region covered by this paper, though Packard 
(1867, p. 279) reports Eugyra glutinans (Moller), under the name 
" Glandula glutinans Moller" from Labrador, "Henley Harbor, 6f. 
sand," (subsequent records, Packard, 1891, p. 396, and Whiteaves, 
1901, p. 271, the latter under the name Eugyra glutinans, are based 
only on Packard's original record). Eugyra glutinans is widely 
