SOME PUGET SOUND ASCIDIANS. 591 



Test : Leathery, about i mm. thick and very uniform through- 

 out. Surface closely beset with short, conical, acute processes, 

 the bases of which are nearly equal in thickness to the height ; 

 many of these processes are single, but others have one or sev- 

 eral smaller ones arising from their bases (PI. XIX, Fig. i6). 



Mantle : Moderately developed, not quite as thick as the 

 test ; longitudinal and circular muscle layers about equal in 

 thickness ; the longitudinal fibers somewhat stronger and ar- 

 ranged in bands more distinctly than the circular fibers. 



Branchial Apparatus : Siphons prominent, strong, branch- 

 ial bent over to nearly a right angle with the antero-posterior 

 axis of the body ; atrial nearly erect, the two of about equal 

 size ; branchial distinctly four-lobed, atrial two-lobed. Atrial 

 orifice surrounded by a row of processes similar to but distinctly 

 larger than those covering the entire surface of the test. Branch- 

 ial tentacles very large, about i8 in number, 13 large ones with 

 smaller ones scattered irregularly among the larger, grouped 

 somewhat in the region of the dorsal tubercle. The numerous 

 large branches of the tentacles themselves bearing short secon- 

 dary branches, or processes (PI. XIX., Fig. 20). Dorsal tu- 

 bercle conspicuous ; mouth of the hypophyseal duct with long 

 horns produced into a double, inturned spiral, one horn with four 

 turns, the other with about six (PI. XIX., Fig. 17). Branchial 

 sac with nine folds on each side, each having sixteen to 

 eighteen bars ; from three to five, usually four, bars between the 

 folds ; transverse vessels of four sizes, usually arranged in the 

 following manner : the space between two vessels of the first 

 order is divided into two parts by a vessel of the second order ; 

 each of these spaces is again divided by a vessel of the third 

 order, and each of these four last spaces is crossed by a vessel of 

 the fourth order ; so that between two of the broad vessels of the 

 first order there are seven smaller vessels. The meshes contain 

 about eight to sixteen stigmata each. The whole structure of 

 the sac rather irregular (Plate XIX., Fig. 18). Dorsal languets 

 consisting of a row of large, closely placed ones situated along 

 the right margin of a broad dorsal area in which there are no 

 stigmata ; and of numerous smaller accessory ones scattered 



