438 
Proceedings of the Royal Society 
AP = a , BQ = b. Then, by expressing that CP and CQ coincide 
in direction, we have at once the equation 
Y . [a + aU(p - a)] [fi + bU(p - /?)] = 0 , 
in which the above results are included as a very particular case, 
and whose geometrical interpretation is elegant. It is a mere 
Scalar equation, since Ya/3 is a factor of the left side, and may be 
omitted. 
Added, May 4 th, 1871. — I have just been informed by Professor 
Cayley that the above results, so far as they concern the Cartesian 
Ovals, are to be found (some actually, some virtually) in Chasles’ 
Apergu Historique , a work of which, to my great regret, I have 
never been able even to see a copy. 
The following Gentleman was elected a Fellow of the 
Society : — 
John Smith, M.D., F.R.C.S.E. 
Monday , ls£ May 1871. 
Dr CHRISTISON, President, in the Chair. 
The following Communications were read : — 
1. On the remarkable Annelida of the Channel Islands, 
&c. By W. C. MTntosh, M.D. 
The extraordinary richness of the littoral region and the 
deeper water surrounding Guernsey and Herm, as well as the 
marked southern character of many of the Annelidan types, formed, 
for instance, an excellent comparison with the ample series of 
specimens which the dredgings of Mr Jeffreys in the Shetland seas 
had lately brought before us ; or, again, with the valuable collec- 
tions procured during the expeditions of the “ Porcupine,” in 1869 
and 1870, the former chiefly from the Atlantic, the latter from the 
same region and the Mediterranean. 
The object of the present paper is to give a short notice, chiefly 
