228 Bibliographical Notices. 



Por the general student the usefulness of the Catalogue is greatly- 

 increased by the succinct account, which is given at the beginning, of 

 the organization of the Hydroida, an account which, as is stated, is 

 mainly drawn from the Rev. Thomas Hincks's ' History of the 

 British Hydroid Zoophytes,' on the plan of which work the present 

 Catalogue is largely modelled. Many interesting facts, based on the 

 author's own observations, are incorporated with this portion of 

 the Catalogue, such, for example, as the occurrence in species of 

 Sertularia (S. crenata) of an intrathecal ridge, a structure chiefly 

 characteristic of the Aglaophenian section of the Plumularidse ; and 

 the extreme variability in the nature and position of the external 

 apertures in the sarcothecae of AglaojyJienia. 



Though the introductory^ renmie of the chief features of hydroid 

 organization was by no means intended to be exhaustive, y^et it is to be 

 regretted that no mention has been made bj^ Mr. Bale of the neuro- 

 muscular or epidermo-muscular cells in the account of the structure 

 of Hydra on the one hand, or of the nervous system of the Medusa- 

 persons on the other. 



As regards the distribution of the species, which have hitherto 

 been obtained almost entirely from the eastern part of the continent, 

 two distinct areas exist, one on the north-east, the other on the 

 south-east, in each of which the forms differ almost entirely from 

 each other, though mixing to some extent in the intermediate 

 districts. 



Thirty- well-marked species occur only in the north-east region, 

 though four of these are found also in districts north of Australia : 

 and eighty species are found only in the south-east region, many 

 of them ranging to Africa, Europe, and America, and occurring 

 more abundantly in New Zealand, with the Hydroid fauna of which 

 that of the south-east region is very closely allied. Two species 

 only, Idia pristis and Plumidaria campamda, occur in both regions. 

 No genera are peculiar to the northern region ; but Limolaria with 

 two species, Malicornojysis, Eucopella^ and Ceratella with one each, 

 are found only in the southern district, together with that section 

 of Plumidaria in which only one hydrotheca is borne on each pinna, 

 of which section one of the species, P. ohllqua, occurs also in Eng- 

 land and Tasmania. 



A list is given of the principal works in which Australian species 

 have been described, together with a more detailed list of the more 

 important general works on the Hydroida which are quoted or 

 alluded to in the text. 



The systematic treatment of the genera and species forms the 

 greater bulk of the volume ; and an idea may be formed of the 

 contribution which Mr. Bale has more directly made to the know- 

 ledge of the hydroid fauna of the Australian seas, when it is noted 

 that, out of about 125 well-defined species which are recorded, not 

 fewer than 47 have been made known by him. 



Counting the undetermined species of Eudendrium and ITaUcium, 

 144 species in all are described, of which about 16 are regarded as 

 doubtful. One species of the genus Hydra is recorded, for which 

 the order Eleutheroblastea, following the older classification, has 



