312 



RUDOLF RUEDEMANN 



carapace to about one-fifth of the length of the carapace from 

 the posterior border. The median line is marked behind the 

 cervical fold by a distinct depression extending about one-third 

 of the distance toward the posterior border. 



Horizon and locality. — -Permian (Enid formation), near Elkeno, 

 Okla. 



Note on identification with A pus. — The writer is well aware that 

 considering the enormous stretch of time from the Permian to 

 the present time, and further the fact that only the carapace of the 



Fig. I 



Fig. 2 



Fig. I. — Apus beedei sp. nov. The two specimens seen obliquely from above and 

 the front. Natural size. The type-specimen is on the right. It shows the trans- 

 versal wrinkle in the place of the cervical fold, portions of the frontal part of the 

 carapace and the median depression. 



Fig. 2.— Apus beedei sp. nov. Lateral view of the type-specimen. X3. Shows 

 the shell-gland and posterior emargination. 



Permian form is now at hand, there is a great possibility that if 

 the body of the animal were preserved, differences of generic 

 importance might be quite apparent, e.g., such as now separate 

 Lepidurus from Apus and which consist in the different develop- 

 ment of the post-anal plate. It could, therefore, be urged that 

 this Permian form should be made a separate genus on theoretic 

 grounds. In such an attempt it would, however, be found that 

 the carapace of the older form is not distinguishable from that of 

 the recent type and the new genus would have no diagnosis, but 

 only its .great age to stand on. It is, however, to be understood 



