vol. 2,pt. 2.] A TAXONOMIC STUDY OF THE SALPIDAE METCALF. 113 



There are no ganglionic outgrowths, but the gland shows the usual 

 condition, consisting of a disk-shaped chamber on each side, con- 

 nected by a convoluted tube with the pharyngeo-eloacal chamber. 



The test protrudes to form several pairs of spines (fig. 104), a large 

 postero-lateral pair containing a considerable tube of mantel epithe- 

 lium, a smaller lateral pair dorsal to these, into the base of which there 

 is a faint evagination of the mantle, and a weakly developed anterior 

 pair, at the angles of the mouth, which show a distinct mantle evagi- 

 nation and but slight protrusion of the test. T3iese structures are 



a.r. 



Fig. 106.— Thalia democratica, solitary form, dorsal view of atrial musculature. The atrial 

 siphon was cut on the ventral mid line, and the left flap thus formed is laid out laterally, 

 the right flap is omitted. from streiff (1908). 



doubtless comparable to the postero-lateral protrusions of Thetys 

 (fig. 114, p. 122) and Ritteria hexagona (fig. 35, p. 63) and to the 

 numerous "tentacles" of Traustedtia (pi. 14). 



THALIA DEMOCRATICA, aggregated zooid, Atlantic Ocean form. 



The asymmetry of the aggregated Thalia democratica is slight 

 (fig. 107, B) being noticeable chiefly in the asymmetrical position of 

 the cloacal aperture and the presence of a lateral protuberance of 

 both test and mantle on one side of the posterior end of the body, 

 much as in Salpa maxima (fig. 67, p. 85). 



There are four body muscles, continuous across the dorsal mid line, 

 but widely interrupted ventrally. I, II, and III are in contact on 

 the dorsal mid line. Muscle IV is branched, as the last body muscle 

 is in the aggregated zooids of other species. Its posterior branch is 

 delicate. It passes by the base of the atrial siphon, but docs not 

 extend more than halfway around the latter. Of course, then, it 

 does not meet its fellow of the opposite side or form any visceral 

 muscle. 



The intermediate muscle is well developed (figs. 107, A, and 108). 

 It is divided into an anterior and a posterior division. The posterior 

 of these arises a little at one side of the mid-ventral line, in front, and 



