REPORT ON THE TUNICATA OF PLYMOUTH. 65 



meshes were totally devoid of stigmata, as in Pharyngndicfyon 

 mirabile of the '' Challenger " collection, described by Herdman,"^ 



I am obliged, therefore, to conclude that Syntethys Hehridicus 

 actually possessed, as Forbes and Goodsir stated it to possess, a 

 branchial sac containing about thirteen transverse rows of oblong 

 stigmata, and presenting a " hooked fleshy tubercle '' at the junc- 

 tion of every longitudinal and horizontal bar. 



It should be noticed that in the original description there is 

 nothing irreconcilable with the view that the branchial sac of 

 Syntethys Hehridicus may in reality have been quite destitute of true 

 internal longitudinal bars, and possibly of horizontal membranes ; 

 the " hooked fleshy tubercles " may have been such rudimentary 

 connecting ducts and bars as Herdman has described and figured for 

 Tyiohranchion speciosiwi (1. c, p. 161). In this connection I may 

 state that I find the internal longitudinal bars of Diazona violacea to 

 be by no means rarely incomplete in portions of the branchial sac ; 

 they are then represented by structures which could well be described 

 as " hooked fleshy tubercles.^' 



I will not maintain that this new view of Forbes and Goodsir's 

 very " remarkable invertebrate " is probable, but it is at least 

 possible. If it should prove eventually to be correct, a very 

 interesting' connection between Diazona violacea and Tyiohranchion 

 speciosiim will have been established. 



By admitting the above-named differences between the branchial 

 sacs of Diazona violacea and Syntethys Hehridicus, it will be noticed 

 that I do not accept Alder's identification of his Guernsey speci- 

 mens of Diazona with Forbes and Goodsir's species. From Alder's 

 account I have been led to believe that he assumed this identity 

 too hastily. He states that his specimens were " at once recognised 

 as the Syntethys Hehridicus of Forbes and Goodsir," and upon this 

 assumption he endeavoured to find out what structural difi^erences 

 there might be between this form and the Diazona violacea so 

 admirably described by the great French anatomist. His researches 

 were not very fruitful of result : '^ The only difference I can find is 

 that the papillae of the branchial sac in the latter {Syntethys 

 Hehridicus) are stout and obtuse, very different from the slender 

 pointed form represented by Savigny ; I have therefore determined 

 to consider them distinct until further observations decide the 

 point." 



Now Alder's Guernsey specimens are certainly identical (speci- 

 fically) with the forms investigated by myself, and they are both 

 fi'om practically the same region of the English Channel ; there is 

 further no appreciable difference between the Plymouth forms and 



* Herdman, "Challenger" Report, vol. xiv, pt. xxxviii, p. 155. 

 NEW SERIES. — VOL. 11, NO. I. 5 



