REPORT ON THE TUNICATA OF PLYMOUTH. 65 



zooids, where they remain sterile or, more rarely, give rise to 

 new buds. 



The partial imbedding of the posterior ends of the zooids in a 

 basal mass of test is a character which is common to this genus and 

 the genus Stereoclavella, as recently denned by Herdman (1. c, 

 pp. 160, 161); but although this is the only character by which 

 Stereoclavella has been as yet distinguished, a comparison of Pycno- 

 clavella aurilucens with the described species of Stereoclavella shows 

 that marked differences exist between the two genera. In Pycno- 

 clavella the zooids arise by slender stalks from the common basal 

 test, and there is a definite demarcation between the two regions ; 

 while in Stereoclavella* it is almost impossible to speak of the 

 common test as a distinct structure. The elegant and regularly 

 clavate form of the free portions of the zooids, together with their 

 delicacy and small size, are also points clearly separating the former 

 genus from the species of Stereoclavella. It appears to me to be 

 very probable that the chief character common to these two genera 

 has been attained independently in each case, Stereoclavella having 

 arisen from a species of Glavelina resembling C. lepadijormis in form 

 and size, while Pycnoclavella is more akin to C. producta. 



2. Pycnoclavella aurilucens, sp. nov. (PI. II, figs. 2 and 3.) 



Colonies very variable in shape and size, as regards both the 

 thickness and extent of the common test and the length of the free 

 portions of the zooids. 



Zooids with thorax slightly compressed from side to side, almost 

 as broad as long, connected with the basal test by a slender cylin- 

 drical foot-stalk of varying length ; thorax -i- inch in length ; foot- 

 stalk from twice to ten times as long. Abdomen elongate, deeply 

 embedded in the common basal test. 



Colour. — A band of golden-yellow pigment extends along the 

 ventral side of the thorax and is continued into the oesophageal 

 region ; it is absent from the dorsal side ; this band gives a 

 conspicuous colouration to the zooids, when seen alive with the 

 naked eye. 



* The preliminary description given by Professor Herdman of 8. australis 

 has no reference to the exact character of its common test. 



