VOL. 2, M. 2.] A TAXOKOMIC STUDY OF THE SALP1DAE METCALF. 103 



of the lower lip, described by Streiff, and his "SegelmusJcel" ["A"] 

 are not represented in any of my numerous specimens. In the char- 

 acter of its oral musculature in the solitary form, Iasis zonaria is the 

 most aberrant of all the Salpidae, great reduction having occurred, 

 and a new muscle (xx) being added. Both lips are strongly and 



FIG. !<2. Iasis ZONARIA, SOLITARY FORM, A SAGITTAL SECTION OF THE ANTERIOR PART OF THE BODY. 

 X 4 DIAMETERS. (DRAWN BY HOYT S. HOPKINS.) 



equally inturned to serve as valves. The upper lip is somewhat 

 inturned, though less than the lower lip, in some other species (see 

 Salpa maxima, aggregated, fig. 69, p. 88, Thalia democratica, solitary 

 and aggregated, fig. 104 B, p. Ill, also figs. 105 and 108). 



The musculature of the atrial siphon (fig. 93), in all my specimens 

 agree, except for minor detail, with Streiff's description. There is a 



a.s.z. 



a.s.r 



as. s 





Fig. 93.— Iasis zonaria, solitary form, dorsal view of the right side and a little of the left 

 side of the atrial musculature, the atrial siphon being cut lengthwise on the ventral mid 

 line and the flaps so formed spread out lateeally. x 13i diameters. modified from streiff 

 (1908). 



strong atrial retractor muscle (a. r.) on each side running to near 

 the angle of the atrial opening. The ventral lip of the atrial opening 

 bears three sphincters. The first of these (v. s. 1), admarginal, is 

 continuous with the admarginal sphincter (a. s. 1 ) of the dorsal atrial 

 lip. The second ventral sphincter (v. s. 2) extends forward, crossing 

 the atrial retractor near its distal end. Near the angle of the atrial 



