500 Sir Norman Lockyer and Dr. W. J. S. Lockyer. [June 14, 



condition has been evolved from the eleutherorhabdic condition, since 

 in this species both ciliated discs and organic interfilamentar junctions 

 are present. 



Anomia aculeatads of no less interest, since it differs from the other 

 species of Anomia examined, and resembles the rare Dimya, in that 

 the gill filaments are not reflected, i.e., they have no ascending 

 portions. 



A very careful examination was made of the gills of Vesicomya and 

 Euciroa, which were said by Dall to exhibit close resemblances with 

 those of the Protobranchia. Both prove to be of the synaptorhabdic 

 type, and their superficial resemblance to the Protobranch gill is due 

 to an expansion of the interlamellar edge of the filaments, a feature 

 which is by no means confined to these two genera. 



Evidence is also adduced to show that the forms included by Pelse- 

 neer in his order Septibranchia are, at least so far as can be judged by 

 their branchial organs, degenerate Molluscs of the Lyonsiella type, and 

 the suppression of the Septibranchia as a distinct order is advocated. 



" On some Phenomena which suggest a Short Period of Solar and 

 Meteorological Changes." By Sir Norman Lockyer, K.C.B., 

 F.E.S., and William J. S. Lockyer, M.A., Ph.D., F.E.A.S. 

 Eeeeived June 14, — Bead June 19, 1902. 



In continuation of the inquiries referred to in a former paper on 

 Indian rainfall and solar activity,* attention has more recently been 

 devoted to an examination of the variations of pressure over the 

 Indian and other areas. 



1. It is well known that in India during the summer months (April to 

 September) and during the winter months (October to March) low and 

 high pressures respectively prevail. In the case of the latter, the 

 pressure is found to exhibit very remarkable and definite variations, 

 and is in excess, every 3J years, on the average, while at these times 

 of excess of high pressure the low pressure during the other 6 months 

 of the year is deficient ; so that every 3J years or so the high pressure 

 becomes higher and the low pressure is not so low as usual. 



2. Further, this short-period variation, which appears in the mean 

 variation of pressure over the whole of India, is as well defined in the 

 mean values for individual stations, such as Bombay (fig. 1, Curve F), 

 Calcutta, Madras, Nagpur, &c. 



3. The view that the variation of pressure in question over India and 

 its neighbourhood is not due to local causes, but is produced by some 



* ' Roy. Soc. Proc.,' vol. 67. p. 409. 



