TRANSACTIONS OF THE SECTIONS. 107 
thickness of the bones of the head are doubtless for the support of the large teeth 
which are developed as these animals attain their adult age. The author observed, 
that this was a good instance, as showing the necessity of studying all kinds of 
animals in all their stages of growth, and under different circumstances. He stated 
that no species could be said to have been properly observed until all these cireum- 
stances had been examined and noted; and that though the notice of a single 
individual or state of an animal was useful, it could only be regarded as a sign- 
post, indicating the existence of an animal which required further study and 
examination. He then proceeded to speak of the African Crocodile. He observed, 
that Adanson mentioned three crocodiles as found in the Senegal. Cuvier, in his 
monograph, thinks that Adanson had made some mistake, and makes some very 
severe remarks on the inaccuracies of travellers; but more recent researches had 
shown that in this case the traveller was correct, and the philosopher at fault. 
Adanson mentions the Green and the Black Crocodiles and the Gavial of Senegal. 
There can be no doubt, from the West-African specimens which are in the British 
Museum, that Cuvier was right in regarding the Green Crocodile as the crocodile 
also found in the rivers in the northern and southern parts of Africa. Cuvier, on 
the other hand, considered the Black Crocodile of Adanson was identical with the 
Alligator with bony eyebrows found in South America. This is not the case; for 
there is a Black Crocodile found in West Africa, which is often imported into 
Liverpool; and there are specimens in the British and Liverpool Museums, and 
some young ones living in the Zoological Gardens in the Regent’s Park: it is a 
true crocodile, but peculiar from having three long plates in the eyelids; and it was 
probably this peculiarity that misled Cuvier. It is to be observed, that the French 
naturalists have not yet discoyered this fact; for the author stated that he had 
recently purchased from the French Museum the skeleton of this African Black 
Crocodile under the name of Alligator palpebrosus from the Brazils; and there was 
little doubt that it must have been the examination of the skull of this animal that 
induced some zoologists to believe that some specimens of alligators had the teeth 
sometimes fitted into notches in the margin, as in the crocodiles, while in fact they 
were observing the skull of a true crocodile, and not an alligator. The Gavial of 
Senegal, of Adanson, is most like the Crocodilus cataphractus of Cuvier, which has a 
long nose like a gavial, but is a crocodile: this animal has been redescribed under 
yarious names. Dr. Gray stated that the crocodiles of India had been much mis- 
understood ; some authors said the common crocodile of Africa was found in India, 
others confused more than one species under the name of C. palustris. There are four 
species found in India: two are confined to the estuaries or the mouths of rivers, 
where the water is brackish,—as Crocodilus porosus or biporcatus, which is found on 
all parts of the coast and also in the islands of Jaya and Borneo, and eyen on the 
north coast of Australia ; the other is a new species, confined, as far as we at present 
know, to the coast of Pondicherry. The latter is only known, from a specimen 
lately received (French), as Crocodilus biporcatus. The other two are confined to 
the inland rivers; and they are sometimes found high up in the mountains, where 
the water of the river is frozen. It is to be observed that these river-crocodiles, 
which have been confounded with the African kinds, are known from them by the 
short, broad shape of the intermaxillary bone, which is separated from the maxilla 
by a straight suture, while in the crocodiles of the African rivers the intermaxillary 
bone is produced behind and between the edge of the maxilla. One species is 
generally distributed over distant parts of India; the other is confined to Siam, 
and is probably the animal described by the French missionaries, though the speci- 
men in the British Museum has no crest on the occiput; but the author believes. 
that this may be either an effect of age or an individual peculiarity. 
On the Production of similar Medusoids by certain Hydroid Polypes belonging 
to different Genera. By the Rey. T. Hrycxs, B.A. 
The author’s object in this paper was to put on record the remarkable fact, which 
had lately come under his observation, that the Tubularian polypes, Stawridia pro- 
ducta (Wright) and Coryne eximia (Allman), produced Medusoids which at the time 
of detachment were undistinguishable from one another, 
