222 J. MURRAY ON GASTROTRICHA. 



excessively difficult to see, and the authors of species may have 

 overlooked them. 



There is no more definite character for distinguishing species 

 of Chaetonotus than the form of the dorsal plates, if one could 

 only see them, but nothing has astonished me more than the 

 utter invisibility of those plates, till some accident, such as finding 

 an empty skin or mutilated specimen, has revealed them. 



As I have put some work into the preparation of this key, and 

 do not wish to throw it away, I have made some use of the 

 material by indicating for the genus Chaetonotus certain groups 

 of species characterised by the possession of some common 

 feature. 



Chaetonotus. 



Body covered by Plates or Scales. 



G. acanthodes, acanthophorus, arquatus, brevispinosits, chuni, 

 entzii, erinaceus, heterochaetus, hystrix, larus, linguaeformis, macro- 

 chaetus, maximus, octonarius, ornatus, persetosus, ploenensis, 

 pusillus, schultzei, serraticaudits, similis, simrothi, spinifer, squam- 

 matus, succinctus, tabidatus, tenuis, uncinus, zelinkai. 



Stated to have no Plates. 

 G. enormis, formosus. 



Nothing said about Plates. 



G. bogdanovii, dubius, gracilis, jamaicense, longispinosus, 

 marinus, slackiae, spi?iulosus. 



With Cephalic Shield. 



C. entzii, erinaceus, formosus, maximus, ornatus, persetosus, 

 pusillus, schultzei, tenuis, zelinkai. Not noted for the other 

 species. 



Head not Lobed. 



G. bogdanovii, dubius, jamaicense, marinus, ornatus, slackiae, 



tabidatus. 



Head Three-lobed. 



G. brevispinosits, chuni, erinaceus, formosus, heterochaetus, 

 hystrix, larus, linquaeformis, macrochaetus, pusillus, schultzei, 

 serraticaudus. 



