DISTRIBUTION IN SPACE. 1(51 



A trophosome (without gonangia) collected by Dr. Hancy at the Cape of Good Hope, and now 

 in ]\Ir. Rusk's collection, is, as I have already said, indistinguishable from that of our common 

 Scrtularia puwila, while this species with its gonangia occurs in the New Zealand collection 

 already referred to, and— judging from the trophosome, for no gonangia are present — it also 

 occurs, as stated above, among some hydroids obtained by Dr. Scouler in California. Indeed, 

 Sertularia pumUa and Lafoea diimosa appear to be the only species yet discovered common to the 

 Atlantic and Pacific shores. 



If these determinations be accepted, Serhilarella jjolj/zonias, Sertularia operculata, and Seriu- 

 Inria jnimila have quite a cosmopolitan range. Resides those now mentioned, including the 

 exceptionally large number of European species which occur also in South Africa, some others 

 have been recorded from other parts of the Southern Hemisphere, but the evidence of identity 

 does not appear to me sufficient for acceptance. We should bear in mind too that in many cases 

 the specimens brought to us from abroad are entirely destitute of their gonosome, and without 

 this important element of identification om* determinations, though we may fairly assume their 

 correctness, are scarcely otherwise than provisional, even though the trophosomes may present a 

 complete agreement. 



The parts of the world from which the most abundant data have been obtained for the 

 establishment of definite provinces of hydroid distribution are found in the North Atlantic and 

 its great eastern offset, the Mediterranean. 



When we compare the hydroids of the Rritish seas with those which have been recorded 

 from the Scandinavian shores as far even as the North Cape, and from the shores of Relgium 

 and the Atlantic shores of France and Spain, we find such a uniformity in the hydroid fauna of 

 the whole of this coast-range that its division into distinct hydroid provinces cannot be thought 

 of. The same group of forms, with but little variation, may be also traced westward across the 

 North Atlantic, by the Faroe islands, Iceland, Greenland, Labrador, Newfoundland, and Nova 

 Scotia. On tlie coast of the State of Maine a decided change begins to show itself by the 

 introduction of many species unknown on the eastern side of the Atlantic, and the difference 

 becomes still more marked as we proceed southwards along the Atlantic shores of the United 

 States, until in South Carolina and Florida — judging from the species enumerated by McCrady 

 and Agassiz — not a single hydroid has been found which can be referred to a species known to 

 inhabit the eastern shores of the Atlantic.^ 



Within the range now mentioned two distinct hydroid faunas may be distinguished. One 

 of these may be followed along the whole of tiie western shores of Europe round to the North 

 American shores by Greenland and along the coasts of the intervening islands, until it attains 

 its south-western hmit a little to the south of Nova Scotia. 



A comparison of the hydroid dwellers in this northern, north-eastern, and north-western 

 Atlantic area with those which have been recorded from the Atlantic shores of North America, 

 between the State of ]\Iaine and the southern point of Florida, shows that though there is a con- 

 siderable number of species common to the two, there are yet so many forms which are special to 

 this more southern area, that we are justified in regarding this portion of the Atlantic shores of 



^ Alexander Agassiz has given a very full list of Noitli American hvdroids, including both the 

 fixed trophosomes and such free hydroid medusfe as have not yet been traced to their trophosomes. 

 ' lllust. Catal. North American Acalephae/ p. 222. 



