Professor T. Rupert Jones — N. American Odracoda. 401 



foot in 3,400 years. Mr. Charles Davison (Geol. Mag., December, 

 18S9, p. 411) gives reasons for thinking a foot in 2,400 years more 

 }»r()bable. Now if we take tlie average of these estimates, and make 

 allowance for the probably more rapid lowering of the bed of 

 a river in its earlier history, as well as steeper parts, we might 

 take 2,500 years per foot as the index of erosion for the Bovey 

 stream in its upper course. As shown on the map the old river 

 gravel stands at an elevation of 750 feet, while the present height 

 of the river at that point where it changed its course is 630 feet, 

 so that it might be taken that it has followed its present course 

 west of the Cleave for some 300,000 years. Yet this is but a short 

 stage in its history, for from data used by Professor Sollas in his 

 address to Section C at the Bradford Meeting of the British 

 Association, it must be some 3^ millions of years ago since this 

 same stream was helping to fill up the Eocene lake and depositing 

 the material that is known as ' the Lignite formation of Bovey 

 Tracey.' 



V. — Notes on Dr. G. F. Matthew's Cambrian Ostracoda from 

 North-Eastern America. 

 By Professor T. Rupert Jones, F.E.S., F.G.S. 



FOR many years Dr. G. F. Matthew, of St. John, New Brunswick, 

 has given much attention to the geology and fossils of the 

 districts lying on or near the north-eastern seaboard of North 

 America, and has closely studied their minute fossils resembling 

 (if not identical with) varieties of small bivalved Entomostraca ; 

 and he has published his results from time to time in the scientific 

 periodicals of Canada and the United States. 



One of the first of his descriptive memoirs on these peculiar 

 microzoa is in the Transactions of the Royal Society of Canada, 

 vol. iii, 1886, and treats of some of these remarkable little organisms 

 from the St. John's Group of Cambrian strata, at pp. 61-66, 

 figs. 16-21, under the names of Lepidilta, LepidiUa, HipponicJinrion, 

 and Beyrichona, some being regarded as Ostracoda and others doubt- 

 fully as Phyllopoda. They were referred to in the Reports British 

 Association, 1889, p. 174, and too hastily supposed to be possibly 

 opercula of Pteropods; they must evidently be accepted as members 

 of the Ostracodous group. 



The terminology used by Dr. Matthew for these little organisms 

 can be readily collated and fitted in with the descriptive terms 

 used by other palaeontologists for similar or allied forms. The 

 modifications of the ovate-oblong valves and of their relative 

 convexity are not strange, except that the ventral border in some 

 of these forms is very much expanded obliquely downwards and 

 backwards, becoming more or less triangular. The ' ocular tubercle ' 

 is high up in the antero-dorsal corner or angle of the valve ; and 

 is often accompanied or surrounded by a circular indication of 

 what Dr. Matthew regards as the mark of the anterior adductor 

 muscle. The central muscle-spot, common in the Leperditian familjs 

 is not recognized. Most of the described specimens the author 



DECADE IV. VOL. IX. NO. IX. 26 



