340 On Phoca caspica and Plioca groenlandica. 



bones agree with the corresponding bones in a skeleton of 

 Phoca caspica of about 12 decim. length (to the tip of the 

 tail), -with tibia of 151 millim. and femur of 82 millim. and 

 67 millim. (as above). Although this difference of ossifica- 

 tion may depend on several other differences, the question thus 

 arose whether the subfossil bones did not belong to Phoca 

 caspica or perhaps to an extinct and hitherto unknown 

 variety of Phoca fcetida^ in which the degree of ossification 

 corresponds nearly with the general growth. 



There is no doubt that Phoca caspica and Ph. fcetida^ 

 although different (c/. Kadde, ' Reisen S. O.-Sibirien,' i. 

 p. 296), are very closely related*, and in the opinion of 

 many authors they should be regarded as varieties of one and 

 the same species. Unfortunately, hitherto, so far as I know, 

 only their external and cranial characters have been studied, 

 but in the other skeletal parts there may be found some 

 features which may throw more light on the question of 

 their relation to each other. So it will be seen that Phoca 

 caspica^ although land-locked, presents itself as an inter- 

 mediate form between Ph . fcetida and Ph. grcenlandica, which 

 latter, from its habitat, as is known, has received its syno- 

 nymic name oceanica. 



In most of the cranial characters, and tliose of the chief 

 importance, as, for instance, in the form and direction of the 

 cristge frontales externa^ (linete semicirculares), in the breadth 

 of the interorliital septum, in the form and connexions of the 

 nasal bones, it is easy to see that Phoca groenlandica comes 

 midway between Ph. vitulina and Ph. Jcetida^ and that Ph. cas- 

 pica is intermediate between yce//c/a and groenlandica. Still 

 more is this last fact to be observed in the characters of the 

 pelvis and the hind limb ; but here Phoca groenlandica and 

 Ph. caspica in many respects form a group together, distinctly 

 separated from the other two species, for besides the above- 

 named proportions of tibia and femur, in the adult state they 

 both have the tibia very much longer than the pelvis as well 

 as than the skull, and their foramina obturatoria are propor- 

 tionately longer and narro^\er, always (at least in the adult 

 slate) longer than the length of tiie pelvis in front of them. 

 'Ihe most evident specific differences between caspica and 

 groenlandica are to be found in the skull, which in Phoca 

 caf-pica has most of the characters of Phoca foetida save the 

 form of the hind palatal margin, which lacks the sharp median 



* As regards the chaiacters cited by the authors as common to Phoca 

 casjnca and Ph. foctida, 1 will only remark that the tuberculum ante- 

 orbilale is sometimes wanting in both these species. 



