276 GEO. H. HORN, M. D. 



DYTISCIDAE. 



While on a visit to Dr. Sharp I was enabled through his kindness to 

 examine very nearly all of the species described by him from our fauna. 

 From notes made by me at the time I have been enabled to identify very 

 many of the species since my return, although a good number still remain 

 unknown to us. 



The work of Dr. Sharp is the most important ever given to science 

 on this family. Numerous characters overlooked by others have been 

 clearly presented. While I can hardly agree with him in his estimate 

 of the value of very minute characters for the separation of species, it 

 must nevertheless be admitted that his entire work gives evidence of 

 close, conscientious and accurate study. 



The following notes are intended to bring his work into closer corres- 

 pondence with our cabinets as far as I am able to interpret it. In those 

 cases in which I feel compelled to dissent from his views I have endeav- 

 ored to give my reasons as clearly and briefly as possible, and if the 

 expressions are short and didactic, they have been so framed to avoid 

 unnecessary verbosity. 



In using Dr. Sharp's work I have many times had occasion to regret 

 that his idea of the entire inviolability of the original name given by 

 preceding authors has been put in practice. Unless there happens to be 

 a new species on a given page it is impossible to say with certainty what 

 genus is before us, nor can we in this case be certain as on p. 411 a new 

 Antiporus is described with the name Hydroporus. It is, to say the 

 least, a little confusing to find, as on p. 271, four generic names on one 

 page. 



The omission of author's names after genera throughout the book is, 

 to say the least, inconvenient. While I admit that the name of the 

 author is not an essential part of the generic name it very often gives us 

 a clue to bibliography, often a matter of very great utility. 



CANTHYDRUS Sharp. 

 This contains the species formerly in our lists under Suphis. 

 C. punctipennis, Shp., seems merely a pale form of bicolor, Say. It 

 is taken frequently by Mr. Ulke near Washington. 



HYDROCAKTHUS. 



Dr. Sharp is willing to admit three species in our fauna. 

 H. oblongns, Shp. — This species is founded on the pale or ferrugi- 

 nous specimens often found in Pennsylvania. 



11. tricolor, Say. — Dr. Sharp identifies as wo have done. 



