324 VOXAGE OF H.M.S. CHALLENGER. 



are sharp, curved, and compressed. Short colic caeca are present. 1 There is no expansor 

 secundariorum muscle. The termination of the tendon of the tensor patagii brevis 

 is never quite simple, and may become very complicated. There is no accessory head 

 to the semi-tendinosus. The ambiens muscle (only absent in Pelecanoldes) always 

 crosses the knee. The number of cervico-dorsal vertebras is not less than twenty-two. 

 The clavicles have only a very small symphysial process. The leg is shorter than the 

 wing. The tarsus is not larger than the mid-toe (except in Procellaria), and is 

 shorter than the ulna. It is never twice as long as the femur. The tibia is only a 

 little, or not at all, longer than the humerus or manus. The basal phalanx of the 

 middle toe is shorter than the two next joints. Basipterygoid facets may or may 

 not be present, and the same is true of the uncinate bone. The humerus, radius, and 

 ulna have a shape different from that of the Oceanitidae. The form of the nostrils, and 

 of the posterior margin of the sternum, varies extensively. The gluteus primus is always 

 very small, and there is a peculiarly formed patagial slip derived from the biceps muscle. 



" Thus in spite of the general superficial resemblance of the Oceanitidae to the smaller 

 forms of Procellariidae, with which all ornithologists previous to Garrod had confounded 

 them, the differences between the two families are, it will be seen, numerous and 

 important. The special points of resemblance which the Oceanitidae have with such 

 Procellarian genera as Procellaria and Cymochorea — such as the general small size, 

 style of coloration, form of skull, comparative simplicity of the tensor patcigii arrange- 

 ment, simple sternum and syrinx (the last three peculiarities being also common to 

 Pelecanoldes) — may best be explained by supposing that these small Procellarian forms 

 are on the whole less specialised than the larger ones (Fulmars, Albatrosses, Shearwaters, 

 &c), and so retain more of the characters possessed by the primitive and now extinct 

 common form from which both the Procellariidae and Oceanitidae must have been 

 derived." 



The Oceanitidae are a small and on the whole compact group, with but few differences 

 of importance between the four genera contained in it. These genera are Garrodia, 

 Oceanites, Pelagodroma, and Fregetta. 



" The Procellariidae, comprising as they do by far the greater number of species and 

 genera of. the group, show much more divergence inter se than is the case with the 

 Oceanitidae." 



They are divided into two groups, of which the Diomedeinae or Albatrosses, 

 containing the three genera, Diomedea, Thalassiarche, and Phazbetria, are the more 

 aberrant, and present the following peculiarities : — 



1 Halocyptena is apparently an exception to this rule, but as Cymochorea has only one citcum, there is nothing 

 surprising in the reduction being carried a step further. As therefore all the congeners of Halocyptena have caeca, it 

 may be safely assumed that their disappearance in it has been very recent, and has occurred since it acquired the 

 rest of its Procellarian characters. This loss of cieca therefore by it does not in any way really approximate it to the 

 Oceanitidae. 



