116 THE ZOOLOGIST. 
Duncan and W. Percy Sladen. The recent and fossil species of Celo- 
pleurus and the recent forms of Arbacia examined, present some structural 
details of both primary and secondary classificatory importance which have 
been hitherto neglected and unrecorded. The ambulacral plates differ 
from those of all other Echinoidea in the arrangement of the triplets, there 
being a central primary plate with an adoral and an aboral demi-plate, 
while there are no additional plates near the peristome in the species of 
Arbacia. The structure of the sutures, especially of the median inter- 
radials, is a modification of the dowelling whieh has been described in 
Temnopleurus by one of the authors. The double optic pore notieed by 
Loven occurs in the fossil species of Celoplewrus and in C. Maillardi, 
a recent species. The authors compare the different forms, and exclude 
Arbacia nigra from the genus Arbacia. The next part will deal with the 
classification. 
Mr. W. F. Kirby read a paper “On the employment of the names 
proposed for Genera of Orthoptera previously to 1840.” The author shows 
the application of every name proposed from the time of Linné to the 
publication of Serville’s ‘ Histoire Naturelle des Insects Orthoptéres,’ and 
appends a bibliography. 
February 19.—Prof. P. Martin Duncan, F.R.S., Vice-President, in the 
chair. 
The Rev. L. Martial Klein, D Sc., of St. Asaph, was elected a Fellow. 
Mr. Thos. Christy exhibited some samples of excellent silk from 
Auckland, New Zealand, but the insect which had spun them was not 
identified. 
The substance of Part III. of the Rev. A. Eaton’s Monograph on the 
Mayflies (Ephemerida) was read by the Secretary. In this the fourth 
series of Group 2 of the genera are dealt with. Among miscellaneous 
representatives of the genera, adult and in good condition, Cloéon is easily 
distinguished by the absence of hind wings; Callibetes by the large 
rounded costal projection and numerous cross veinlets of its broad, oblong, 
obtuse hind wings; Betis by hind wings as broad and obtuse as those of 
the preceding genus, but with the costal projection, if any, small and acute, 
and with scarcely a cross veinlet at all; Centroptilum by the extreme 
narrowness of its very small hind wings, and usually by the slenderness of 
their costal projection. The distinctive characteristics of Sections 10 and 
11 of the genera are also taken into consideration, and full descriptions of 
many new species are given. 
A paper was read by Prof. P. Martin Duncan, “ On the Anatomy of 
the Ambulacra of the recent Diadematide.” The author described the 
arrangement of the compound plates of the genera Diadema, Echinothria, 
Centrostephanus, Astropyya, Micropyga, and Aspidodiadema. The first 
