2i8 AYERS AND JACKSON. [Vol. XVII, 



ending in a very sharp point. This tooth prevents the forward 

 slipping of any object which is being subjected to the rasping 

 action of the ventral teeth. 



The ventral teeth are arranged in four rows, two upon each 

 side of the dental plate (PI. XXII, Fig. 6 ; PI. XXIII, Fig. lo). 

 The larger rows are anterior and external. Each tooth is some- 

 what conical, with a large hollow base, and a smaller apical 

 portion which is somewhat flattened laterally. The free distal 

 portion of each tooth curves upward, backward, and inward, 

 tapering to a sharp point. The teeth of each row are united 

 firmly to their bases, the corneous material of the teeth being 

 continuous through an entire tooth row. The separate rows 

 are not united in any way. Occasionally, however, the ante- 

 rior and the posterior teeth of the row are not fused with the 

 remainder. The teeth in each row decrease in size from before 

 backward. They are yellowish-brown in color, and the number 

 of teeth varies to a considerable extent. 



In the following tables the formula used to indicate the 

 number of teeth in the several rows is given in the subjoined 

 diagram : 



Left outer row. 



Left inner row. 



Right outer row. 



Right inner row. 



The limits of the variability in the teeth of Bdellostoma, so 

 far as known, are as follows : 



Bdellostoma from the Cape of Good Hope (Muller), 6 to 7 

 p-ills s U 11 1 1 1 12 1 12 



giiis, Tjr|3, iilii' ll|l2- 



Bdellostoma from the coast of Chili, 10 gills, V-|-V" 

 (Lacepede), \\\\\, \\\\%. 



Bdellostoma from the coast of California, 11 to 13 gills, 1 1 1, 



11 I 12 



11 I 11- 



In the California series examined by Dr. Ayers the dental 

 formulae were as follows : In 22 individuals with 1 1 gills, 



110 19 110 19 zL 1 I 1 1 1_0 I 10, 1 10. I 10, 1 11 I U. 

 -*• ""9" I "9' -"- TO I T "0' ^ '9"r9' -^ 9' I 10' ^ 10 110' ^ 10 I 9' 



1 10 111 1 1 I 1 1 A 1 1 I li) 1 11 1 10 5 11 I 11 1 11 I 11 

 ^ "9 1 ~9"' -"- T'O I TO' ^TollO' ^ llllO' " lOllO' ^ llllO' 



1 12 I U 2 12 112 

 ^ 9' I ^9"' "^ 11 I 11- 



