J 18 THE ZOOLOGIST. 



and thus enable a comparison to be made with existing sponges to which 

 generically they mostly belong. In all 43 genera and 113 species have 

 been recognized by their characteristic spicules. Many of the forms have 

 not hitherto been known as fossil. The existing relatives of. many of them 

 now inhabit the Indian and Southern Oceans, but some are at presant only 

 known from the North Atlantic. The remains of deep-water sponges are 

 intermingled in the deposit with others hitherto supposed to belong to 

 moderate depths only, but in recent dredgings by H.M.S. 'Egeria' off the 

 S.W. coast of Australia, at a depth of 3000 fathoms, there is a corresponding 

 admixture of similar spicules. 



Zoological Society of London. 



Feb. 2, 1892.— W. T. Blanford, Esq, F.R.S., F.Z.S., in the chair. 



The Secretary read a report on the additions that had been made to the 

 Society's Menagerie during the month of January. 



Mr. W. Bateson exhibited some crabs' claws bearing supernumerary 

 prongs. It was shown that these extra parts are really complementary 

 (right and left) pairs of indices or pollices, according to their position of 

 origin, and not repetitions of the two pincers of the claw, as was commonly 

 believed. 



Mr. Sclater made some remarks on the breeding of the Ground-Pigeons 

 (Geophapes) in the Society's Gardens, and showed that the young of these 

 pigeons, when first hatched, were not materially different in point of develop- 

 ment from those of the typical pigeons, and that there was consequently no 

 ground for separating the Geophapes from the order Columba on this 

 account, as it had been recently proposed to do. 



A letter was read from Prof. K. Ramsay Wright, enclosing some photo, 

 graphs of the heaps of skulls of the American Bison which are collected on 

 the plains of the Saskatchewan, and piled up at the sidings on the Canadian 

 Pacific Railway, awaiting transport, and which testify to the enormous 

 number of these animals recently exterminated. 



Mr. W. Bateson gave a summary of his recent observations on numerical 

 variation in teeth. The facts given related chiefly to specimens of Quadru- 

 mana, Carnivora, Marsupials, and other orders of Mammals in the British 

 and other Museums. The author pointed out that the ordinarily received 

 view of homologies between teeth is based on the hypothesis that the series 

 is composed of members each of which is either present or absent. In the 

 light of the facts of variation, this hypothesis was shown to be untenable, 

 and an attempt was made to arrive at a more just conception of the nature 

 of the homology of multiple parts. 



Mr. R. Lydekker described part of the upper jaw of a Sirenian Mammal 

 from the Tcrtiarics of Northern Italv, containing milk-teeth. As these teeth 



