PEOPESSOK OWE.V ON CNEMIOEMS. 269 



in Tachyeres \ A second small vacuity weakens the ilium above the hind part of the 

 ischiadic foramen in Tachyeres, as in the White-eyed Pochard {Anas leucophthalnmsy ; 

 but this character is not present in Cnemiornis or in Cereopsis. The proportion in 

 length of the preacetabular to the postacetabular parts of the pelvis is greater in the 

 two last-named genera than in Tachyeres. 



I have nothing to add to the characters of the femur, tibia, and fibula illustrated in 

 my former memoir. The excessive development of the combined pro- and epicnemial 

 processes, which suggested the affinity or resemblance to Colymbus, we now know to have 

 been possessed by a species of another family of web-footed birds. The great extinct 

 Anserine of New Zealand may have kicked its vra,y through the dense element with a 

 vigour and speed that would have arrested the attention of navigators more strongly, 

 perhaps, than such action in the smaller non-volant Lamellirostral which has thereby 

 got the name of " Steamer Duck." 



The three digits whose metatarsal bones coalesce to form the " metatarsus " in birds 

 are homotypes of the three metacarpals similarly fused together in the wing, viz. the 

 second, third, and fourth. The first, sometimes wanting, but more commonly present, 

 keeps its rudimental metatarsal element free in all species with the back toe. The 

 rough slightly depressed surface above the entotrochlea shows the usual anserine posi- 

 tion of attachment of the back toe in Cnemiornis. 



The metatarsus of Cnemiornis (Plate XXXVIII. fig. 12) yields well-marked evidence 

 of its closer affinity to Cereopsis than to Tachyeres or other Lamellirostral genera. In 

 these the entotrochlea, or that distal condyle which supports the second or innermost ^ 

 of the three anterior toes, is given ofi" from the composite bone at a higher or more 

 proximal level than the other two trochlear condyles (ib. fig. 14, ii) : it also projects 

 much more backward than the other condyles. In Cereopsis the entotrochlea (ib. 

 fig. 13, ii) comes off at a lower level, nearly that of the ectotrochlea, and projects but a 

 short way behind the line attained by the hind part of the mesotrochlea, this terminating 

 a little behind that reached by the ectotrochlea. Thus, in Cereopsis, the three trochlese 

 are more in accordance with the ordinary pattern in non-natatorial birds ; and this is 

 precisely the character by which Cnemiornis departs from the web-footed order in the 



' According to Mr. Smit's figure of the pelvis of the Steamer Duck in Trans. Zool. Soc. vol. vii. pi. 62. fig. 59 : 

 the originals, collected at the cost of the nation in a Government expedition, have not found their way to the 

 I^ational lluseura of Natural History. On special application to the naturalist of the expedition of H.M.S. to 

 the Magellan's Strait, some bones of an immature Tachyeres have been sent by him to the British Museum sinee 

 the penning of the present paper. 



^ Nyroca, Plem. ; see Eyton, ' Monograph on the Anatidse,' 4to, 1838, p. 63, and plate. 



' M. Alphonse Milne-Edwards, describing the metatarse of Cereopsis in his ' Eecherches pour servir a 

 I'histoire naturelle des Oiseaux Possiles,' 4to, 1867, writes of the " troohle'es digitales :" — "I'exteme, au lieu d'etre 

 forteraent rejetee en arriere, comme dans les autres Anatides ; se trouve presque sur le meme plan que la 

 mcdiane " (p. 80). I find the " ectotrochlea " (supporting the. outer five-jointed toe) to have its hind border a 

 little anterior to the plane of that of the mesotrochlea, while the entotrochlea projects as much behind that 

 plane, but in a markedly less degree than does the internal trochlea in Tachyeres and other Anatidae. 



VOL. IX. — PART III. May, 1875. 2 o 



