clxxiii 



Communications read and exchanges laid upon the table. 



Mr. Riley exhibited four interesting fresh-water Crustaceans, 

 presented by Mr. J. Boll, who had collected them around Dallas, 

 Texas. One was a fresh-water Shrimp very near the genus 

 Palemon^ found in ponds near Dallas, and the more remarkable 

 from the fact that while Palemon yamacensts was known to 

 occur in flowing fresh-water, no species has hitherto been found, 

 so far as he was aware, in standing water ; another was an inter- 

 esting and probably undescribed species of Branchipus, also 

 found in ponds ; a third was a species belonging to the curious 

 genus Arguhis^ which is remarbable for the large carapace or 

 shield, its rudimentary abdomen, and by the second pair of legs 

 being transformed into two large suckers, by means of which the 

 animal attaches itself to the gills of the gar-fish {Leptdosteus 

 ferox), where the species in question is found. Argulus is sup- 

 posed to be parasitic, but Mr. Boll thinks it uses the gar-fish sim- 

 ply as a beast of burden. The fourth was a species of Estheria. 



Dr. G. Engelmann communicated the results of his observations 

 of the temperature of last winter and compared it with previous 

 winters during the last forty years : 



December, 1874, . . 35°.3 December, mean of 40 years, 33°. 2 



January, 1875, . . . 2i°.3 January, " " 32°.o 



February, '• . . . 24°.2 February, " " ZS^-Z 



Winter 1874-75, • • • 26°.9 i Winter, " " 33°.5 



This table shows that the first winter month, December, was over two 



degrees milder than the average; but January was io°.7 and February 



even i i°.i colder than the average, so that the low temperature of the past 



winter is entirely owing to the low temperatures of January and February. 



In the last forty years we have experienced only four winters in which 



the mean temperature fell below 30 degrees, viz. : 



1855-56 . . 26°.4 1872-73 • • 26°.3 



1871-72 . . . 29°.! 1 1874-75 • • • 26°. 9 



In the first and last of these four winters the low temperature was owing 

 to the excessive cold of January and February (to which a very cold March 

 succeeded) ; in the third winter December and January were the cold 

 months, and in the second all three months were very cold, but none so 

 excessive as in the other three winters. 



It appears that three of the coldest winters of forty years occurred within 

 the last four years, with a milder one (1873, 79°-34°-8) between them. The 

 other cold winter dates back nineteen years; no winter was colder than 

 30°.5 ; in the winter of 1837-38 there was an extremely cold February, 

 while December and January ranged above the average. The question 



