104 EINAE LONNBERG, MAMMALS COLLECTED BY THE SWEDISH ZOOLOGICAL EXPEDITION ETC. 



In the smaller and younger specimen the ascending processes of the premaxil- 

 laries extend further backward beyond the end of the nasals, but in the largest 

 (= oldest) specimen the nasals reach about as far back as the premaxillaries. The 

 former condition prevails in Fornarina which thus in this respect represents a more 

 juvenile stage than Heterocephalus. 



If Ruppell's figure of the skull of H. glaher is correct my specimens differ 

 widely from that species with regard to the situation of the palatine foramina which 

 in the former are situated chiefly in front of a line drawn across the palate as a 

 continuation of the pheripheric contour of the zygomatic arches. In my specimens 

 these foramina are situated behind such a line in the same way as in Fornarina 

 according to Thomas' figure^ of the latter. But, although the situation of these 

 foramina thus far is alike in my specimens and in Fornarina, there is another quite 

 important difference between them. In the latter, according to Thomas' figure, the 

 suture between the premaxillary and the maxillary extends across the palate at the 

 anterior end of the palatine foramina, but in my specimens the corresponding suture 

 is seen at the posterior end of the foramina in question. These foramina are also 

 very small in my specimens their length being about 1,5 mm. 



Concerning H. dunni Thomas writes as follows: » Incisors enormously thick and 

 large, far heavier than in any other member of the group. » — - — — »c6mbined 



breadth of upper incisors 3,o». — In my largest specimen the incisors are still 



larger and heavier measuring as much as 3,3 mm. As the type of H. dunni is said 

 to be old and the length of its head and body is about 10 mm. more than that of 

 my biggest specimen this difference in the combined breadth of the upper incisors 

 appears to be of importance. The size of the incisors in H. glaher appears to be 

 rather constant and not increase much with age, because Thomas says that the 

 study of immature and old specimens of that species has shown to him »that no such 

 development of the incisors occurs in old age in that animal » . That is, the incisors 

 do not increase in size with age so that they become so big as those of H. dunni. 

 In the present specimens on the other hand, a very striking increase in size of these 

 teeth takes place. In the smallest and youngest of my specimens the combined 

 breadth of both incisors is only 2,i mm., in the next 2,4 mm., in the third 2,8 mm., 

 and in the biggest 3,3 mm. If only one of these younger and smaller specimens, and 

 the biggest had been collected, it would have appeared rather probable that these 

 specimens represented two different races, a small and a large, because the dissimil- 

 arity is so very obvious and even the smaller looks rather adult thanks to its lamb- 

 doid crest. With the intergradation exhibited by all four specimens it is impossible 

 to believe in such a theory, and the gradual development of the incisors is quite 

 clear. But then, when nothing of that kind of development is to be seen in H. glaher 

 as quoted above, these specimens cannot be referred to that species. Other differences 

 from the same, in addition to different shape of the zygomata and the situation and 

 size of the palatine foramina, are the greater length of the nasals, the longer diastema 

 and the greater occipitonasal length of the skull. 



1 1. c. PI. LIV, fig. 4. 



