66 REPORT ON THE TUNICATA OF PLYMOUTH. 



Savigny's species. Therefore Alder's examples must also be 

 referred to the species Diazona violacea. 



The absence of any indication in Alder's paper that he re-examined 

 the " portion of a specimen (of Syntethys Hehridicus) from the 

 original habitat " which Professor Goodsir sent tu him, renders 

 intelligible what would otherwise have been a very strange omission 

 on his part. I refer to his failure to notice the i-emarkable discre- 

 pancy between the structure of the branchial sac in the Channel 

 specimens and that described for Syntethys Hehridicus. 



Thus, although I quite agree with Alder that there is as yet no 

 sufficient ground for generically separating these two forms, I 

 believe Forbes and Goodsir's species to be perfectly distinct and 

 to possess the following distinguishing characters : 



Orifices not divided into lobes, evenly rounded. 



Zooids projecting freely by their thoracic portions, which are 

 united to the common mass by a slightly contracted but not pedun- 

 culated oesophageal region. 



Branchial sac with thirteen transverse rows of oblong stigmata ; 

 a hooked interserial papilla (connecting duct) at the intersection of 

 every longitudinal (interstigmatic) and transverse bar. 



Oviduct absent (?) 



But the whole matter is so beset with doubts that it is greatly 

 to be desired that specimens should be obtained again from the 

 Hebrides, and their anatomy re- described. Unfortunately Giard 

 gives no anatomical details of the Diazona dredged by him and 

 described in Comptes Rendus, ciii, p. 755. 



DESCRIPTION OF PLATE II. 



Illustrating Mr. W. Garstang's " Report on the Plymouth Tunicata," 



pt. 1. 



N.B. — Where not otherwise stated all the figures were drawn from preserved material. 



Fig. 1. — Clavelma lepadiformis, 0. F. Miiller. Three of the dorsal lauguettes of the 

 branchial sac. Zeiss, A, Oc. 2, Cam. 

 d.s. = Dorsal sinus. 

 A.»j. = Horizontal membrane. 



Fig. 2. — Pycnoclavella aurilucens, gen. et sp. nov. Portion of a colony. A section has 

 been taken through the colony in order to show the common test and the imbedded por- 

 tion of the zooids. Nat. size j slightly diagrammatic. 

 p.^. = Common test. 

 ^.^. = The free portions (thoracic and ossophageal) of the zooids projecting from the 



common test. 

 u.^. = Tbe visceral portions of the zooids imbedded in the common test. 



