14G 



THE VOYAGE OF H.M.S. CHALLENGER. 



Cynthiidae. I am inclined to regard these as typical Molgulidte which have reverted to 

 the ancestral form of branchial sac, rather than as forms derived immediately from the 

 common ancestors of IMolgulidse and C3-ntliiid8e at or near the point 0., because they 

 exhibit in all their other organs highly differentiated Molgulid characters.' 



The ancestral Cynthiidse after the separation of the primitive Molgulidje (0. in 

 table, p. 150) were continued onwards with little change to the Cynthinae (the genera 

 Cyntliia and Microcosmus) of the present day. The remaining sub-family, the 

 Bolteninse, must be placed on a side branch which diverged from the early Cynthin?e. 

 In this ancestral line a jjart of the test became enlarged and prolonged to form a well- 

 marked peduncle (Fig. 27), thus leading to the genus Boltenia, while Cidcolus a,nd 

 Fungulus are degenerate deep-sea forms characterised by that peculiar modification of 

 the l)ranchial sac (see Fig. 28) found in the more primitive Bathyoncus, and in Pharyn- 



FiG. 27. — Cvkolus v:tirUUi. 



godictyon in the Polyclinidaj. In CvJeoh'S, however, curious calcareous spicules are 

 found strengthening the vessels of the branchial sac (Fig. 28, $]:>.). 



' See tliis Report, Part If. Appendix A., p. 402. 



