364 Mr. A. H. Hassall's Catalogue of Irish Zoophytes. 



stinct species, and to whom we are indebted for almost all we know 

 of the anatomy of the Ascidian type of zoophytes. 



Some time since, I forwarded to Dr. Johnston specimens under 

 the name of Bowerhankia densa for examination : one of them was in 

 fact Valkeria imbricata in the primary stage of its growth, that is, 

 spreading over a plain surface ; the other was elevated in the form 

 of a distinct polypidom, the condition in which V. imbricata is 

 usually met with. I remarked on these specimens somewhat to the 

 following effect, not at the time recognising them as belonging to 

 the species Valkeria imbricata, that they represented the species 

 Bowerbankia densa, and that it did not always confine itself to the 

 surface of the object upon which it grew, but sometimes rose from 

 it as a separate polypidom. Dr. Johnston remarked upon them, that 

 they represented " the species in its perfect state." In another 

 letter Dr. Johnston writes, " Accidentally viewing your specimens of 

 Bowerbankia densa, var. ramosa, it at once flashed on my mind that 

 they were Valkeria imbricata, which is indeed the fact. Bower- 

 hankia densa and Valkeria imbricata, are they not states of one and 

 the same species ? Your observations will probably result in the 

 erasure of a spurious species." I have thus Dr. Johnston's testi- 

 mony in favour of the identity of Bowerbankia densa and Valkeria 

 imbricata*. 



Sea Point, Dublin bay : not common. 



I may here observe, that many species of zoophytes, as well as 

 the above, spread over the surface of attachment in a single layer, 

 prior to becoming elevated into separate and independent polypi- 

 doms. This with many species appears to be a law of their growth, 

 and is very obvious in the Flustras. 



V. pustulosa. Not common : Dublin Bay. 



Langenella repens. Some weeks ago I forwarded a zoophyte to 

 Dr. Johnston which I conceived might be Langenella repens. Dr. 

 Johnston observed on the specimen sent, " This may be Langenella 

 repens, but it is not so like as to make one certain ; your conjecture 

 is very probably correct, and then it throws light upon a thing 



which has puzzled us If you will turn to my figure of Flustra 



membrariacea, you will find some processes or tubes figured, which, 

 in the description, are left undecided as to their nature. These I 

 now consider to belong to Langenella repens, or an allied and soli- 

 tary species." Since the receipt of the letter containing the above 

 observations, I have made a particular examination of these tubes, 

 and have arrived at the conclusion that they are not zoophytes at 

 all. On Flustra membranacea the tubes are unconnected with each 

 other, and appear to form shut sacs, no opening being visible at 

 either end, and certainly none is present at its free extremity. Their 

 bases are fixed to the back of the polype cells, and each tube is 

 filled in a recent state with a clear fluid. The use of these processes 

 on Flustra membranacea appears therefore to me to be still involved 

 in obscurity. Plate VIII. fig. 3. represents a few of the cells of the 



' * The cells of Valkeria imbricata first manifest themselves on the main 

 stems as mere buds or protuberances, and in this stage of their formation 

 are iniperforate. 



