NATURAL SCIENCES OP PHILADELPHIA. 301 



Mr. Joseph Willcox stated that he had observed lately the 

 flight of grasshoppers in Colorado. On a cloudy afternoon the 

 insects were on the wing, high in the air, in countless multitudes. 

 A party of several persons were riding in a carriage and the ques- 

 tion of probable rain was discussed. Suddenly the grasshoppers, 

 with great unanimity, descended to the ground, the scene remind- 

 ing one of a furious snow-storm. In two or three minutes no 

 grasshopper could be seen in the air, and in a short time it com- 

 menced to rain. Soon after the rain ceased to fall, the insects 

 took flight again, but in the course of half an hour, without any 

 particular indication of rain, they suddenly plunged to the earth 

 again. Soon after this it rained again. This process was re- 

 peated three times on that afternoon, and each descent was fol- 

 lowed by a fall of rain. 



Genesis of Gassidaria striata, Lam. Mr. Gabb called atten- 

 tion to a series of specimens illustrating the genesis of a recent 

 species of mollusk. About 1850, Geo. B. Sowerby described a 

 fossil from the Miocene formation of Santo Domingo, under the 

 name of Cassidaria laevigata, which differed from the recent form 

 C. striata, Lam., in being a much more solid shell, with a broader 

 body whorl, with decided varices, more expanded outer lip, mark- 

 edly produced in a posterior lateral direction, little or no trace of 

 teeth on the inner lip, and with a polished surface, or showing only 

 obsolete traces of striation on the adult shell. The young speci- 

 mens, however, are always striated, the inner lip is more or less 

 crenulated, and the outer lip is not so expanded as in the adult. 

 On comparing adults of laevigata and striata, no conchologist 

 would hesitate for a moment in calling them distinct species. 

 Later, a form was described by R. J. L. Guppy from a deposit in 

 Jamaica, of the same geological age as the Dominican beds, and 

 which differs in the adult stage from the Dominican fossils in 

 having the juvenile characters persistent ; that is to say, the 

 spire is higher, the not very strong striation covers the body 

 whorl, the thinner inner lip is crenulated throughout its entire 

 length, the outer lip is less expanded and the three varices are only 

 visible externally as trifling irregularities of the lines of growth, 

 although they show internally as perfectly formed lips. This 

 form was called by Mr. Guppy G. sublaevigata, but in 1873, Mr. 

 Gabb called attention to its small points of difference and reduced 

 the name to the grade of a synomyn of laevigata. 1 Later, Mr. 

 Gabb has discovered, in the Pliocene deposits of Costa Rica, an- 

 other shell, in which the progression of characters is continued. 

 The spire is still higher, the lips less crenulated, the varices 

 suppressed, the surface striation more marked, and, in short, the 

 Costa Rica shell can hardly even be called a variety of C. striata, 

 so close is it to the living species ; and yet the connection between 



1 Tr. Amer. Philos. Soc. 1873, p. 222. 

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