THE ASCIDIANS 249 



constriction mentioned in the diagnosis. The absence of this latter 

 character in D. inartnattan may be inferred from Lahille's statement 

 that the digestive tube does not differ here from the ordinary Didemmi?7i 

 form. One might doubt the constancy of this character in D. stran- 

 gulatinn^ but for the fact that it is present in zooids not yet fully grown. 

 From all that can be learned from the material available, it seems that 

 the abdomen, cut aw^ay from the thorax at this point, becomes freed 

 from the test in some vs^ay, and so liberates the embryos into the water. 

 I have been able to pick out a number of such severed abdomens from 

 the test, where they lay merely embedded in shallow pits in the sur- 

 face layer. 



D. strangidatum is also rather closely related to D. cereui7i Giard, 

 but is readily distinguished from this species by its narrower branchial 

 and longer atrial siphon and by its peculiar recto-esophageal neck. 



The specific name chosen has reference to the cutting off of the isth- 

 mus that connects thoi'ax and abdomen. 



Kadiak Island, Alaska, July 3, 1899. Dredged in St. Paul harbor 

 in about twenty fathoms. Four colonies in the collection, the smallest 

 about 6 mm. in diameter, all on fragments of molluscan shells. 



AMAROUCIUM TRANSLUCIDUM sp. nov. 



(PI. XXX, figs. 29 and 30.) 



General characters of the colony. — In unusually regular conical 

 masses, the attachment being by the apex of the cone, which generally 

 constitutes a short peduncle. Frequently, several of. these masses are 

 united by their peduncles. Upper surface, forming the base of the 

 cone, gently arched. A longer and a shorter diameter to the base of 

 the cone at right angles to each other. 



Size of largest mass in collection : height 15 mm., greatest trans- 

 verse diameter 20 mm., least 15 mm. Height of all the masses nearly 

 the same, and the other dimensions much more uniform for all the 

 specimens than is usual among a series of specimens of Compound 

 Ascidians. 



Color. — Light red, not confined to the zooids but diffused through- 

 out substance of test. Test unusually transparent for this genus, and 

 the zooids very plainly seen through it. 



Zooids. — Nutnerous, rather large, closely crowded, and regularly 

 placed ; systems hardly recognizable except in young colonies. Com- 

 mon cloacal orifices few, apparently becoming obliterated in the older 

 colonies, rather large and distinct in the smaller ones. About 10 mm. 

 long as measured in the test of preserved colonies, very straight and 



Proc. Wash. Acad. Sci., July, 1901. 



