836 



THETIS SCIENTIFIC RESULTS. 



ull, divided into a fixed peduncular, and a free terminal 

 portion. In P. pecthiata, also, regeneration has occurred in the 

 hydrothecie and sarcothecas much more abundantly than in P. 

 JUicnla, for in the former hydrothecse occur each with as many 

 as tnirteen successive margins. 



In view of these differences, and in spite of the odd variations 

 described by Pictet and Bedot, ^^ I cannot agree to the union of 

 Allman's two species until forms more definitely intermediate 

 are found. 



Dimensions in mm. : — 







Allman's 



Allman's 





"Thetis" 



type of 



type of 



Organs. 



specimens. 



Perisiphonia 



Perisiphonia 







filicula. 



pectinata. 



Peripheral tube, diameter... 



0-05-006 



0-045-0-07 



0-055 



Hydrotheca, length adnate 









to axial tube 



0-33-0-36 



0-38 



0-36(1-38 



Hydrotheca, length free 









from axial tube 



0-13-0-17 



0-14 



0-31-0-322* 

 0-15-0-19 



Hydrotheca, diameter at 









mouth 



0111-0123 



0-117-0-144 



0-084-0099 



Sarcotheca, length^s 



0-07-0-10 



0-055-0-12 



0-150-282* 

 0-120-10 



Sarcotheca, diameter 



0-027 



0-027-0-030 



0-024-0-027 



Distance between adjacent 









hydrothecaa on hydro- 









clades^s _ 



0-46-0-49 



0.39-0-44 



0-62-0-66 



P. filicula I regard as a synonym of Johnson's Cr?/;?^o/aWa 

 ■exierta, of which characteristic figures are given by that author, 

 fi'.^. 3b exhibiting unmistakeably the presence of nemataphores. 

 Tub latter name is prior in time. 



Regarding the relationships of similar forms described by 

 other authors, it is impossible to decide. The general appear- 

 ances of the colonies described as P. pectinaia by Pictet and 



'■^ 3 Pictet and Bedot — Res. Camp. Sci. Monaco, fasc. xviii., 1900, 

 Hydraires, p. 20. 



24 The numerator gives the total length of a hydrotheca or sarcotheca 

 including reduplicated margins, the denominator, the length of the primary 

 hydrotheca or sarcotheca in the same series. 



2 5 From the surface of the peripheral tube to the tip. 



2 6 Measured from any point of one hydrotheca to the corresponding point 

 ■of that next to it on the same side of the axial tube. 



