vol.2, pt. 2.) A TAXONOMIC STUDY OF THE SALPIDAE METCALF. 21 



and C. virgula (pi. 12, fig. 29). The lower lip is inrolled to function as 

 a vtdve, much as in the solitary forni. This valvular action of the 

 lower lip is characteristic of all species of Salpidae, both solitary and 

 aggregated forms, and need not be mentioned in the reference to 

 other species unless it shows some feature of special interest. 



The test in the aggregated form is thicker than that of the soUtary 

 form, but is no less soft. The luminous organ is a single large gland 

 on each side in the interval between the second and third body 

 muscles. 



There are four body muscles (I to IV). There is but a single oral 

 retractor, with which are united the three sphincter muscles of the 

 lower Up (I. 1,1. 2, I. 3). The first sphincter of the upper Up (u. 1) 

 is almost, but not quite, continuous with the retractor. The second 

 and third sphincters of the dorsal lip (u. 2 and u. 3) are united to the 

 intermediate muscle. There is no ventral oral retractor such as is 

 found in the solitary form. The absence of this ventral retractor 

 accounts probably for the difference in the insertion of the third 

 sphincter of the lower Up (I. 3), which in the soUtary individual 

 belongs to the ventral retractor system, but in the aggregated indi- 

 vidual is attached to the single retractor here present. The interme- 

 diate muscle (i. in.) bends backward at its dorsal end and unites 

 with the upper portion of the first body muscle. There is an ap- 

 proach, but no union, of these muscles in the solitary form. The 

 body muscles are much less regularly arranged in the aggregated 

 form than in the soUtary individuals. All are continuous dorsally 

 across the mid line. VentraUy, as in the solitary form, the interme- 

 diate muscle is in contact with its fellow of the opposite side, but it is 

 not continuous across the mid Une. Each is continued ventraUy into 

 the peduncle. In young zooids these anterior peduncle muscles are 

 distinct except that they touch at their tips. In older zooids they 

 are closely appressed from their tips in the peduncle almost up to 

 the mid-ventral Une of the body. The intermediate muscles are 

 therefore distinct, though at first glance in an older zooid they 

 appear united ventraUy. 



The aggregated individual differs from the solitary in having the 

 last body muscle continuous ventrally with its fellow of the other 

 side. The fused muscle (v.) turns forward on the mid line and runs 

 a short distance toward, but not to, the gut. Figure 3 is slightly 

 distorted, showing this part of the muscle as a flat band, rather than 

 a line as it should appear in edge view. 



We find in the aggregated form of this species a muscle not before 

 described, lying on the mid-ventral line, beneath the intestine (v.') 

 We have again distorted our figure to show this visceral muscle as 

 a broad band instead of as a line which would be its true appearance 

 * in side view. Posteriorly the visceral muscle seems to be connected 

 with the funnel-shaped group of connective tissue fibers whose apex 



