vol.2,pt. 2.] A TAX0N0M1C STUDY OF THE SALPIDAE METCALF. 123 



at its other end with the ventral edge of the second sphincter of the 

 lower lip. In the larger specimen (fig. 115) the third sphincter is 

 wholly independent, but its base is connected by a blood sinus with 

 the ventral retractor. In the larger specimen there is an exceedingly 

 delicate first sphincter of the lower lip (Z. 1), admarginal, which 

 arises from the dorsal edge of the dorsal oral retractor. 



The muscles of the upper lip also differ in the two specimens. In 

 the smaller there is a short, but fairly broad, first sphincter (u. 1). 

 In the larger individual no corresponding muscle is found, but in its 

 place is the muscle blood sinus (fig. 115). The second sphincter is 



en. 



Fig. 115.— Thetys vagina, solitary form, oral muscles seen from the right side, x 1A diame- 

 ters. (Drawn by Hoyt S. Hopkins.) 



broad. Like the body muscles, it is interrupted on each side, the 

 interval showing the continuous blood sinus. 



The dorsal horizontal band is short and independent of other 

 muscles, though it is united to the second sphincter of the upper lip 

 by a blood sinus. The intermediate muscle is short in both specimens. 

 It is shorter in the smaller specimen (fig. 114) and is united to the 

 base of the first sphincter of the upper lip. Postero-ventral to the 

 lower end of the intermediate muscle one sees, in each specimen, 

 two very short problematic muscles entirely disconnected. Com- 

 parison with the aggregated zooid (fig. 117) seems to indicate that 

 these minute muscles are isolated ventral fragments of the sphincters 

 of the upper lip. Compare also the conditions in the solitary Salpa 



