XVI 



Annual Report. [February, 1916 



number of endemic species and one endemic genus, the latter 

 being a sponge Cortispongilla. 



To Mr. F. H. Gravely the Society owes an interesting paper 

 on the evolution and distribution of Indian spiders belonging 

 to the subfamily Aviculariinae. Of the eleven groups into 

 which the Aviculariinae have been divided, five occur in the 

 Oriental Region. These are the Ischnocoleae, Thrigmopoeeae, 

 Selencosmieae, Ornithoctoneae and Poecilotherieae. The Isch- 

 nocoleae found in the Indian Peninsula and Ceylon form a 

 very compact group, probably related to those of other parts 

 of the world through their most primitive species only. This 

 group consists of a series of species leading up from these primi- 

 tive ones to the Thrigmopoeeae (confined to the Indian Penin- 

 sula) in which simple stridulating organs appear between the 

 chelicerae and palps. On the other side of the Ganges the 

 Ischnocoleae are almost extinct, having presumably suffered in 

 competition with the Selenocosmieae, a far more highly special- 

 ized group, which appears to have arisen from them in that 

 part of the Oriental Region in much the same way as the 

 Thrigmopoeeae have in the Indian Peninsula. The stridulat- 

 ing organs of Chilobrachys , the most highly specialized genus of 

 the Selenocomieae, are far more elaborate than those found in 

 any genus of the Thrigmopoeeae ; and Chilobrachys, alone among 

 the Selenocosmieae, has spread into the Indian Peninsula and 

 Ceylon. This suggests an explanation for the absence of the 

 Ischnocoleae and Thrigmopoeeae from the northern and eastern 

 parts of the Indian Peninsula, the Parts in which Chilobrachys 

 must have been longest established . The Poecilotherieae do not 

 come into competition with the other groups of Aviculariinae, 

 being arboreal instead of terrestrial in habit. It is concluded 

 that they have originated from the Ischnocoleae as a result of 

 their adaptation to a new environment in the Indian Peninsula 

 or Ceylon, to which they are still confined. Only indirect evi- 

 dence is, however, available either with regard to them or to 

 the Malaysian terrestrial group Ornithoctoneae. In the 

 absence of direct evidence to the contrary it may be supposed 

 that the latter group also originated from the Ischnocoleae 

 in the country which it now inhabits. 



Mr. James Hornell published in the Journal an account of 

 the Recent Pearl Fishery in Palk Bay. The acquisition from 

 the Raja of Ramnad, of his fishing rights on the Indian side of 

 Palk Bav, had permitted a systematic survey being made of 

 the sea-bottom of this region with the result that the existence 

 of two beds of pearl oysters was proved, the oysters being con- 

 fined to the area of a bed of muddy sand between the 5| and 

 5J fathom contours. The oysters from the larger— the Tondi— 

 bed were numerically deficient in pearls, but a small number 

 of pearls were exceptionally large, whilst the oysters from 

 the Kanangadu beds resembled those from Tinnevelly and 



