256 Mr. R. I. Pocock on the Taxonomy 



XLII. — The Taxonomy of Recent Species o/*Liimilus. 

 By K. I. Pocock. 



[Plates V. & VI.] 



Part I. — The Question of Names. 



The existing species of Limuhis are restricted in ran<:^e to 

 the eastern coasts of North and Central America and the 

 shores of the Mahiyan and Chinese seas. Anyone acquainted 

 with problems of geogiaphical distribution would expect 

 to find structural differences of more than specific value 

 between the species inhabitini^ areas so long and widely sun- 

 dered. An examination of all available material has justified 

 this expectation to the full. It has shown that the American 

 form is distinguishable from the Oriental by many points 

 certaiidy worthy at least of generic recognition ; also that 

 the three known species from the Indian seas, while agreeing 

 with one another in the main, are at the same time divisible into 

 two well-marked groups, one of which is typified by L. rutundi- 

 cauda, the other by the two species which currently pass as 

 L. moluccanus and L. Ivmjispina. These two types I have 

 regarded as valid genera, keeping for the latter the name 

 Tachypleus of Leach, and proposing for the former the new 

 name Carcinoscorpius. Furthermore, I have linked these 

 two genera together to form the subfamily Tachypleina?, 

 reserving the name Xiphosurinai for the American genus. 



This division of the old genus into three genera demands a 

 settlement of the question as to which of them should bear 

 the name XiphosurUy of which polyphenius of Linnajus is the 

 type. 



Under the name Monocidus polyphemus, Linnaius (wSyst. 

 Nat. ed. X. p. G34, 1758) confounded two species, namely the 

 American and the Moluecnn, as can be seen from the refer- 

 ences he cites. He may, however, be considered to have 

 himself limited the name to the American species when, in 

 176-i, he definitely described a specimen of that species as 

 poli/phemiis (Mus. Ludovic. Ulr. p. 460). 



This, ])erhaps, was the line taken up by Latreille in 1802, 

 when, by vcatricting the name polypheniaa to the American 

 form, he reversed the action of Lamarck and probably also of 

 Fabricius. 



For the species characterized as Monoculus polyphemus in 

 the tenth edition of the * iSystema,' Gronovius (Zoophylac. &c., 

 Ins. p. 220, 17G4) proposed the name Xiphosura, giving an 



