Plate 18. 



Fig. 1. BotelUna labyrinthica. X 10. Porcupine 51. U.S.N.M. No. 6247, exterior. 

 2. BotelUna labyrinthica. X 10. Porcupine 51. U.S.N.M. No. 6247, longitu- 



tudinal section. 

 3 and 4. BotelUna labyrinthica. X 10. Transverse sections (same station). 



107 



