Bibliographical Notice. 479 



but that to observe accurately, to direct the observation to the really 

 essential points, and to describe perfectly are the most difficult of all 

 arts. Dr. Kroyer rejects the distribution of Copepoda, proposed 

 by Professor Steenstrup and Dr. Liitken (in the Transactions of the 

 Koyal Danish Society of Sciences, division of Natural History, fifth 

 series, fifth volume, 1861), into three groups according to whether 

 the females have but one external oviduct, or two such containing rows 

 of round eggs, or, finally, two external oviducts containing but one 

 row of disk-shaped eggs. To this classification Dr. Kroyer very pro- 

 perly objects that the groups thus formed do not correspond to 

 any typical or important peculiarities of structure, nor does it even 

 fulfil the requirements of a mere registration of species, as it applies 

 only to the females, and as there are not a few Copepoda without 

 any external oviducts at all. It may indeed be said with good reason 

 that the males, preserving as they do the original type more purely, 

 would afford better characters for groups and genera than the females, 

 of which the often monstrous deformations are chiefly dictated by 

 biological considerations. Dr. Kroyer, in speaking of Lernseopodina, 

 points out how well the generic types within that group are exhibited 

 by the males, and he insists more than once on the merely temporary 

 character of systematic divisions founded on females only. With 

 regard to Thorell's proposition (in the Transactions of the Royal 

 Swedish Society of Sciences) for a division of the whole order, which 

 he calls Copepoda, into Gnathostoma (with free mandibles), Pcecilo- 

 stoma (without mandibles), and Siphonostoma (with mandibles 

 enclosed in a tube), Dr. Kroyer acknowledges that it proceeds on 

 sound principles, but considers that our knowledge of this order is 

 still too limited as yet for the carrying out of such a classification. 

 Faithful to his principles, the author limits himself eutirely to de- 

 scriptions and subordinate points of classification. For the use of 

 those who are not conversant with the Danish language, there are 

 very full Latin extracts of descriptions, definitions of new geuera (of 

 which nine are proposed), and also a Latin explanation of the plates. 

 We shall draw attention to a few particulars. The number of newly 

 described species is ninety-six, of which one has been named by Fa- 

 bricius Condracanthus radiatus, F. ; one, Penicidus clavatus, may 

 coincide with Midler's Lerncea clavata ; thirteen others have been 

 obtained by exchange from the Museum of Vienna, named, but not de- 

 scribed by Kollar, whose names have been preserved ; eighty-one are 

 collected and named by Dr. Kroyer. It may not be superfluous to 

 observe that the species described in this paper as new do not coincide 

 with any of those described by Professor Steeustrup and Dr. Liitken, 

 except in the case of Silenium polynoes, Kr., identical with Herpyllo- 

 bius arcticus, Str., which latter name will have to be cancelled, as the 

 whole description, &c, is founded on an unfortunate fundamental 

 mistake. Dr. Krover opposes the theory of Zenker, that Argulus 

 should either be united to Branchiopoda or form a separate order ; 

 and his views concerning the homologies of the appendices seem to 

 remove the principal difficulties in the way of deciding the place of 

 Argulus in the system. What Milne-Edwards describes as " un 



