40 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



that the muscle we number II joins dorsally muscle III. The three 

 muscles to the post-abdomen are closely similar to those in the 

 aggregated 0. Jioridana. The larger, median one, entering from 

 above, terminates near the base of the post-abdomen, in the loop of 

 the gut (pi. 10, fig. 25). Of the pair of more slender bands, arising 

 from the lower part of the last body muscle, on each side, that 

 on the left side is prolonged almost to the tip of the long slender 

 testis, while that on the right side passes along the caecum and on 

 nearly to the tip of the slender mass of degenerate ( ?) cells. This 

 structure lying at the tip of the caecum is probably homologous with 

 the cells at the tip of the caecum in the aggregated Cyclosalpa virgula 

 and with the organ in the solitary forms of Ritteria retracta, R. picteti, 

 and R. amboinensis, which Ihle regards as a blood-forming organ. 



The peduncle muscles are, first, a fused anterior pair derived from 

 the ventral ends of the intermediate muscles; second, a partially fused 

 posterior pair derived from the ventral ends of the united first and 

 second body muscles; and, third, a median strand arising at the 

 ventral point of the united fourth pair of body muscles and running 

 forward on the ventral mid line, past the third pair of body muscles 

 from which it receives additional fibers, then passing forward, some- 

 times between the separated upper portions of the posterior pair of 

 peduncle muscles, and bending down into the peduncle. 



The muscles of the atrial siphon are as in the aggregated Cyclo- 

 salpa Jioridana, except that there are twice as many of the delicate 

 sphincters. The oral muscles must receive separate description for 

 the younger and the older zooids. In the younger zooids (fig. 22, 

 pi. 8, and fig. 23, pi. 9) there is a well-developed oral retractor con- 

 nected as usual with the first body muscle. Passing forward, 

 this gives rise ventrally, first, to the third sphincter of the lower lip, 

 then to a second ventral branch, the second sphincter of the lower 

 lip, and finally passes into the first sphincter of the lower lip. The 

 first sphincter of the upper lip arises on each side as a branch of the 

 second sphincter of the lower lip. The second and third sphincters 

 of the upper lip unite ventrally to form a common trunk which 

 posteriorly joins with the ventral half of the intermediate muscle, 

 not with the first body muscle. This arrangement of this muscle 

 is comparable with what we find in the aggregated Oyclosalpa pinnata 

 and O. affinis, except that the union of the diagonal strand with the 

 intermediate muscle is further toward the ventral side. It seems 

 hardly natural to call this a ventral oral retractor, for its attach- 

 ments are different, but it functions in much the same way. The 

 dorsal longitudinal muscle band does not extend quite far enough for- 

 ward to come into contact with the fourth sphincter of the upper 



