106 Mr. D’Arcy W. Thompson on new Hydroid 
Sertularia , sp. (PL XVIII. figs. 1, 1 a, 15.) 
Trophosome. Hydrocaulus attaining a height of about four 
inches. Pinnae alternate. Hydrothecae opposite, in pairs, on 
the pinnae ; closely approximated, tubular, rather long, di¬ 
verging for about a third of their length ; alternate, on the 
stem, one in the axil of each pinna; orifice small, with two 
teeth. Colour reddish brown. 
Gonosome. Unknown. 
Locality. Gulf of St. Vincent (Dr. Ferd. Muller). 
I only possess a single small example of this species, unfor¬ 
tunately without gonangia ; and I therefore hesitate, in the 
absence of fuller information, as to giving it a new specific 
name. It may possibly be referable to the genus Dipliasia. 
Sertularia operculata (?). 
Dynamena bispinosa, Gray. 
Dynatnena fasciculate, Kirclienpauer, Nova Acta Acad. Leop. vol. xxxi. 
‘(1863). 
Sertularia bispinosa, Hutton, Coughtrey, &c. 
After a long and careful examination of a very large series 
of specimens, both of the Australasian variety and of the com¬ 
mon British species, I am forced to the conclusion that, as 
yet, we have really no evidence to justify the separation of 
the two forms. 
The present form, whether specifically distinct or not, has 
long been known from southern localities. Dr. Johnston 
examined specimens from the Cape of Good Hope which 
“ differed in no respect from those of our shores.” Prof. 
Busk, in describing the zoophytes of the ‘ Rattlesnake ’ expe¬ 
dition (Macgillivray’s Voy. of the 1 Rattlesnake,’ vol. i. app.), 
says, “ This species occurs in all parts of the world. It is to 
be carefully distinguished from D. bispinosa , Gray, also an 
Australian and New-Zealand species.” But in a report on 
some specimens from South Africa (Brit. Assoc. Report, 1850, 
p. 118), he says “The Sert. operculata of S. Africa is un¬ 
doubtedly the same species as the British, although from a 
rather general deviation from the more usual toothing of the 
margin of the cell, which obtains in specimens from the 
southern hemisphere, this variety has been denominated S. 
bispinosa by Mr. Gray.” Mr. Hincks, also, seems to ac¬ 
quiesce in the above opinion. 
On the other hand, Mr. Gray, as we have seen, unhesi¬ 
tatingly described his specimens as a new species under the 
name of Dyn. bispinosa , and is supported in his opinion by 
Captain Hutton and Dr. Coughtrey. Again, Dr. Kirchen- 
pauer, overlooking Gray’s paper, described the form, of which 
