ZooL.-VoL. III.] HOLMES— ON SPHy^ROMIDS AND DYNAMENE. 299 



referred to, "If an author describes a genus and does not 

 refer to it any species, either then or previously described, 

 the genus cannot be taken as established or properly de- 

 fined, unless the characters given have an unmistakable 

 significance." The definition of Dynamene, I believe, may 

 be reasonably held to fulfill this requirement. The genus 

 is characterized along with other genera from which it is 

 accurately distinguished, so that there would be little diffi- 

 culty in recognizing it even if species were not subsequently 

 assigned to it by Leach himself. The original definition of 

 the genus is as follows: "Eyes not reaching the anterior 

 margin of the first segment; base of tail on each side with 

 two equal foliaceous appendages, apex of the tail emargin- 

 ate; nails bifid. There are several indigenous species of 

 this genus, but the characters are not yet determined." 

 Essentially the same definition is repeated without the 

 assignment of any species in the ' Transactions of the Lin- 

 nean Society ' for 1818, but in the ' Dictionnaire des 

 Sciences Naturelles ' (t. 12, 1818) the genus is again de- 

 fined and three species are assigned to it, Montagui, rubra, 

 and viridis in the order named. 



The name Dynaniene may be further objected to on 

 account of being nearly identical with Dynamena, which 

 was described a few years before. How near one name 

 must be to another to be rejected is a question which most 

 codes of nomenclature leave to the discretion of individual 

 writers. Are we to discard, as some writers do, such 

 names as Platynierus because it is preoccupied by Platy- 

 mera ? or reject both because there is a still earlier name 

 Platymeris ? This is a subject concerning which it is un- 

 fortunate that different usages prevail, for this circumstance 

 promises to give rise to much confusion when the validity 

 of generic names is more critically looked into than is 

 usually done at present. Names like the above, as well as 

 numerous undoubted synonyms, have been suffered to 

 stand simply because they have been neglected; but sooner 

 or later judgment will be passed upon all such names, and 

 the result will be that a large share of existing genera will 



