vol.2, pt. 2.] A TAX03ST0MIC STUDY OF THE SALPIDAE METCALF. 159 



The name Cyclosalpa, based upon the arrangement of the zooids 

 in the stolon in whorls, probably does not appropriately apply to the 

 Cyclosalpae asymmetricales, and it would seem more natural to place 

 these two species in a distinct subgenus, but the very close relatin- 

 ship between the species bakeri (asymmetrical) and floridana (sym- 

 metrical) is an obstacle to such division of the subgenus. 



The scheme of relationship figured shows the Cyclosalpas as the 

 primitive members of the family, from which two major divisions 

 have descended. The more primitive species, with elongated intes- 

 tine at least in the solitary forms, may be called the DOLICHO- 

 DAEA. These are the Cyclosalpae. The species with a very com- 

 pact gut forming a spheroidal mass in both solitary and aggregated 

 forms may be named the SPHAERODAEA. This group includes 

 Apsteinia and Salpa. The species with a curved gut, which, however, 

 at least in the solitary individual, does not form a close "nucleus," 

 may be called the CIRCODAEA. This group includes Brooksia, Rit- 

 teria, Iasis, Thetys, Thalia, Pegea, and Traustedtia. It is a much 

 less compact group than either the Dolichodaea or the Sphaerodaea. 

 This division, on the basis of the condition of the gut, seems accu- 

 rately to express true relationship, but practically it is not so con- 

 venient as might be wished, for those of the Circodaea, which have 

 a more compact gut, approach rather too closely for casual discrimi- 

 nation the condition of the Sphaerodaea. 



Iasis and Thalia agree in the valvular character of the dorsal lip 

 of the atrial siphon and the development of the dorsal atrial sphinc- 

 ters as a plexus. They also agree in the reduction of the neural 

 gland in their aggregated zooids. In Iasis (fig. 103, p. 108) it is a 

 median chamber with right and left lobes and a single lateral duct, 

 while in Thalia it is wholly absent. In Thetys the neural gland is 

 a single median chamber (fig. 118, p. 126). Because of the resem- 

 blance in their neural glands and larger eyes in the aggregated zooids, 

 Iasis and Thetys seem to be somewhat near relatives, in spite of the 

 great difference in their muscles. Thalia seems much more nearly 

 related to Iasis than to Thetys. 



Among the Circodaea there is greater instability of the muscular 

 system, the eyes, and the neural glands. The musculature is over- 

 emphasized in the Ritterias, the more primitive members of this 

 division, while in the more aberrant forms, Pegea and Traustedtia, it 

 becomes much reduced. The term OLIGOMYARIA might well be 

 limited to these two subgenera. ^ 



The eyes of the aggregated zooids become increasingly degenerate 



in the more aberrant forms. The aggregated Iasis and Thetys show 



the dorsal eye very compact. Degeneration of the rod-cells begins 



in Iasis and goes far in Thetys. In the aggregated Thalia the apical 



2621— Bull. 100, vol. 2—19 11 



