Naturalization of Dreissena polymorpha. 361 



trees over the water ; it feeds entirely on insects ; it sits on a 

 branch in motionless expectation, and as soon as a fly, but- 

 terfly, or moth, passes by, it darts at it, and returns to the 

 branch it had just left. It seems an indolent, sedentary bird, 

 shunning the society of all others in the forest. It never vi- 

 sits the plantations, but is found at all times of the year in the 

 woods." They are further described to perch in a stiff atti- 

 tude, almost perpendicularly; and to be very silent birds, ex- 

 cept at the season of propagation, when they frequently emit 

 piercing cries. Le Vaillant was informed that they breed in the 

 holes of trees, and lay about four blue eggs ; but this part of 

 their history remains in much obscurity. M. Natterer, who 

 has lately returned from a long residence in the region which 

 they inhabit, will, it is hoped, elucidate all that is yet doubtful 

 concerning them. 



For the tribal group of todies and jacamars, I hesitatingly 

 propose the name Angulirostres, which is little applicable to- 

 the former. 



June 7th, 1838. 



Art. II. On the Naturalization of Dreissena, (Vanbeneden), po- 

 lymorpha, (Pallas), in Great Britain. By Hugh E. Strickland, 

 Esq., F.G.S., &c. 



There are several interesting facts connected with the histo- 

 ry of this mollusc, which deserve to be recorded. The recent 

 date at which it has been introduced, and the rapidity with 

 which it has become diffused over the country, afford some 

 valuable data for scientific inquiry. The zoologist will be led 

 to speculate on the means by which species are transported 

 to distant localities, and on the greater capabilities for emi- 

 gration possessed by certain species and genera, in conse- 

 quence of being more tenacious of life, more accommodating 

 to circumstances, and more prolific, than their congeners. — 

 And although the Dreissena has unquestionably been intro- 

 duced into this country by human agency, yet it might be 

 worth while to enquire how far the same result might have 

 been effected by natural causes alone, such as the drifting of 

 a piece of timber with these shells attached, down one of the 

 European rivers, and across the German Ocean, into some 

 brackish or freshwater estuary on our own coasts. The geo- 

 logist will see the importance of this inquiry, as connected 

 with the distribution of organic remains, and the sudden ap- 

 pearance and disappearance of particular species in a given 

 stratum. 



The Dreissena polymorpha is admirably figured in this Ma- 



n2 



