REPORT ON THE TUNICATA OF PLYMOUTH. 53 



2. Pycnoclavella, gen. nov. 



Der. — TTVKvoc, closely united. 



External appearance. — Zooids small and delicate, clavate, arising 

 by slender stalks from a more or less thick, basilar mass of test- 

 substance. 



Body consisting of a small thorax, a slender, often greatly elon- 

 gate oesophageal region, and a more dilated abdomen, the greater 

 part of which is imbedded in the basilar mass of common test. 



Test thin and delicate around the thorax, thicker and firm in 

 the foot-stalks, dense and cartilaginous throughout the basilar mass ; 

 the latter is traversed in all directions by stolonial tubes, some of 

 which even extend and branch in the oesophageal region of the 

 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 StereoclaveUa, as recently defined by Herdman (1. c, 

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

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

 clavella aurilucens with the described species of StereoclaveUa 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 StereoclaveUa"^ 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 StereoclaveUa. It appears to me to be 

 very probable that the chief character common to these two genera 

 has been attained independently in each case, StereoclaveUa having 

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

 and size, while Pycnoclavella is more akin to G. 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- 



* The preliminary description given by Professor Herdman of S. australis has no refer- 

 ence to the exact character of its common. test. 



