296 Ortmann — Linuparus atavus. 



no chelae were developed, as required by the diagnosis of the 

 family. The following pairs of pereiopods decrease in size and 

 thickness. The fifth pair shows plainly in both specimens the 

 male sexual opening. The distal parts from the merus onward 

 are not present in the fifth pair. 



Traces of abdominal appendages (pleopods) are discern able 

 in both specimens ; the right one of the fourth segment in 

 specimen (a) is the best preserved, consisting of an oval jDlate, 

 which is finely striated. Sexual appendages are wanting. 



Thus we see that the position of this fossil form with the 

 genus Linuparus is warranted not only by the tricarinate cara- 

 pace, but also by other characters of minor importance, such as 

 the distribution of spines on the carapace, the armature of the 

 abdomen (which in its general plan is exactly like that of 

 Linuparus trigonus, and differs from Palinurus as well as from 

 the other genera of the family), and the peculiar shape of the 

 flagella of the antennas. Only the frontal horns differ from 

 those of the living species, but, as I have shown above, they are 

 intermediate between that species and the condition seen in 

 Palinurns, and this difference should be regarded as of only 

 specific value : I do not think the shape of the frontal horns 

 justifies the creation of a new genus, and this would be the 

 only way left, if we do not wish to unite this fossil generically 

 with the living Japanese species. 



Altogether, there is no doubt that the fossil described above 

 is the nearest relation of the living Linuparus trigonus, none 

 of the other living species coming so near to that Japanese 

 Crustacean. This fact is extremely interesting, since it proves 

 that the genus Linuparus only slightly modified existed as far 

 back as the Upper Cretaceous time, and, indeed, one might be 

 induced to regard Linuparus atavus as the direct ancestor of 

 the living species. 



In conclusion, this new fossil gives a hint as to the origin of 

 the geographical range of the genus Linuparus. Linuparus is 

 not — as might be supposed from its present exclusive distribu- 

 tion in the Japanese seas — a form indigenous to that part of 

 the world : the Japanese seas are not the " center of origin " 

 of this genus, but the living species is to be regarded as the 

 only "relict" left from a former wider distribution. Probably 

 this genus (like most of the other Mesozoic marine animals) 

 possessed formerly a more or less cosmopolitan distribution, 

 but it has been restricted gradually, and the only remnant left 

 at the present time is the Japanese Linuparus trigonus, which 

 is to be regarded, accordingly, as a very ancient type among 

 the living Decapods. 



Princeton University, February. 1897. 



