THE VOYAGE OF THE ' CHALLENGER/ 427 



semi-tendinosus muscle has a well- developed accessory head. The ambiens 

 muscle, when present, does not pass over the knee, but is lost on the 

 cueniial process of the tibia. The number of cervico-dorsal vertebrae is 

 twenty-one. The clavicles have a long, curved, symphysial process. The 

 leg-bones are longer than the wing-bones. The tarsus is longer than the 

 mid-toe * and ulna, and at least twice as long as the femur. The tibia is 

 at least twice as long as the humerus, and much longer than the manus. 

 The basal phalanx of the middle toe is as long as, or longer than, the 

 next two taken together. 



The Oceanitidae also agree together in having no basipterygoid pro- 

 cesses, no uncinate bone, a peculiarly short and stout humerus, radius, 

 and ulna, a single circular nasal aperture, a sternum with its posterior 

 margin quite or nearly entire, a larger gluteus primus, as well as in 

 numerous other smaller details already noticed. All these characters 

 never coexist together in any Procellarian form, and, if my observations 

 are correct, the Oceanitidae further differ from the Procellariidae by having 

 a bleeps brachii muscle of the normal form, with no patagial slip. 



The Procellariidae, on the other hand, have the following charac- 

 ters: 



The number of secondary rerniges is never less than thirteen, and is 

 usually much greater. The tarsi are pretty uniformly covered with small 

 hexagonal scutella. The claws are sharp, curved, compressed. Short 

 colic caeca are present t. 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 Pelecano'ides) 

 always crosses the knee. The number of cervico-dorsal vertebrae 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 

 Oeeanitidae. The form of the nostrils, and of the posterior margin of 

 the sternum, varies extensively. The gluteus primus is always very 



t Halocyptena is apparently an exception to this rule, but as Cynochorea has only 

 one caecum, 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 caeca therefore by it does not in any 

 way really approximate it to the Oceanitidas. 



