Miscellaneous, 259 



PROCEEDINGS OF LEARNED SOCIETIES. 



GEOLOGICAL SOCIETY. 



March 25, 1891.— Dr. A. Geikio, F.R.S., 



President, in the Chair. 



The following communication was read : — 



" Notes on Nautili and Ammonites." By S. S. Buckman, Esq., 

 F.G.S. 



1. The Position of the Last Septum. — Mr. Bather's theory of shell- 

 growth in Cephalopoda (Ann. & Mag. Xat, Hist. 1888, 'i. p. 300) 

 seems to depend upon the idea that the last septum in the joung in. 

 Nautilus and Ammonites was always formed at a proportionately 

 increased distance from the penultimate. This supposition is not 

 borne out by specimens of Nautilus, Witchellia, Lioceras, Ludwigia, 

 and Grammoceras examined by the Author. 



2. Shell-muscles of Nautili and Ammonites. — Two specimens of 

 Ammonites in the Author's collection are marked by impressions 

 which seem to indicate the position of tlie shell-muscle. 



May 27, 181)1.— Dr. A. Geikie, F.ll.S., 

 President, in the Chair. 



The following communication was read : — 



" On the Lower Jaws of Procoptodon." By E. Lydckker, Esq., 

 B.A., F.G.S. 



After reviewing Sir R. Owen's writings upon the large extinct 

 Xangaroos for which he established the genus Procoptodon in 1874, 

 the Author describes two mandibular rami from the clay beds of 

 Miall Creek in the neighbourhood of Biugera, N.S.W., which belong 

 to this genus, and from their characters and a comparison of them 

 with the lower jaws in the British Museum, he maintains that this 

 part of the skull indicates two very distinct species of the genus, for 

 which he retains the names P. rapha, Ow., and P. goliah, Ow., 

 though it is possible that the types of those two species are really 

 specifically identical, in which case the name P. ^Jtt^/o, Ow., might 

 have to be adopted for one of the species described. 



MISCELLANEOUS. 

 On a Freshwater Medusa. By Dr. J. v. Kennel. 

 In my ' Biologischen und faunistischen Notizen aus Trinidad ' I 

 alluded to a little Medusa which I had found in considerable num- 

 bers on the east coast of the island in a small freshwater lagoon 

 entirely cut off from the sea. The creatures were altogether absent 

 in the broader portion of the lake near the sea, and were first 

 encountered about fifty paces further inland, where a gentle current 

 was perceptible, and the flora as well as the fauna bore the impress 

 of a freshwater habitat. It is true that Polychaete Annelids and 

 specimens of Mysis were also found in abundance at this spot 

 among the luxuriant Alg?e and freshwater plants, yet the represen- 

 tatives of the small freshwater animals greatly exceeded them in 



