﻿DETERMINATION OF CERTAIN BRITISH GYRINID^. 107 



the interstices are very finely but distinctly punctured, and in the 

 other (b) the same parts are transversely substrigose. Although 

 these insects have been in our lists for more than twenty years, 

 there is still much diversity of opinion as to the names to be 

 applied to them. Dr. Sharp, in introducing the insects in question 

 in his valuable paper on the " British Gyrinidae " (Ent. Mo. Mag. 

 v. pp. 57, 58), adopts the name caspius, Aube, for a, and colym- 

 bus, Er., for b ; but caspius, Aube, which according to authors 

 = caspius, Men., should have smooth interstices, whilst in 

 colymbus, Ei\, the same parts should be extremely finely punc- 

 tured. Dr. Eegimbart is a great authority on these insects, and 

 doubtless has some good reason for treating the two forms under 

 consideration as one species, but certainly none appears from his 

 Monograph ; nor is it clear why the name caspius, originally given 

 to a form with the interstices smooth, should be applied to insects 

 exhibiting respectively two kinds of sculpture on the interstices. 

 Canon Fowler, in ' Col. Brit. Islands ' (vol. i.), includes both 

 forms under the name caspius, Men., at p. 212, and at p. 214 he 

 deals with them under the name colymbus, Er. After copying 

 Begimbart's synonymy and translating that author's description 

 of caspius, Men., he proceeds to examine the characters laid down 

 by authors for colymbus and caspius, and concludes by very . 

 properly proposing a distinctive name for the form b. Under 

 all circumstances it seems to me better to adopt the name 

 colymbus, Er., for a, and striolatus, Fowler, for b; at all events 

 until it is shown, more conclusively than at present, that they 

 ought to bear some other. I have been unable to obtain males of 

 either of these species for dissection, but I have a female of 

 colymbus, Er., taken by myself in the Norwich district. This 

 insect was, until recently, standing amongst my specimens of 

 natator, where it attracted my attention by its less convex forrn, 

 and the straighter sides and more evident outer apical angle of 

 its elytra. 



In re-defining the species which he calls caspius, Menetr., at 

 p. 259 of his Monograph, on the challenge of M. de Borre, Dr. 

 Eegimbart omits all mention of the form with the interstices 

 substrigose. The former writer seems to think that the caspius 

 of Eegimbart, with its varieties, and suffriani, Scrib., are forms 

 of natator, Scop., and he appears to base his opinion on the fact 

 that it is not impossible in some, perhaps in most, specimens of 

 the species last named, with an amplification of about 40 diame- 

 ters, to detect feeble traces of very fine punctuation. For all 

 practical purposes, however, the interstices of natator may be 

 regarded as impunctate. M. de Borre says that he has found all 

 the intermediate forms between caspius and natator, which, 

 assuming that his caspius is the same as that of Aube, is intelli- 

 gible enough ; for it is not clear how the genuine caspius of that 



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