588 CALIFORNIA ACADEMY OF SCIENCES. 20 



related with the decrease in the number of rakers on the 

 anterior limb. 



The scales also become successively larger, from very 

 small ones in ftancispinis to large scales in introniger. 

 But it is impossible to use the size of the scales for the 

 purpose of generic distinction. In the whole genus the 

 transverse rows of scales corresponding in number with 

 the pores are very oblique (making an angle of about 

 forty-five degrees with the vertical) and have rarely, if 

 ever, been counted as the " transverse rows of scales." 

 Besides these there is a series that is actually vertical, 

 making an angle of about forty-five degrees with the 

 former. For each " oblique transverse" row there are 

 two plainly visible vertical rows, and as a scale for each 

 of the latter rows lies upon or nearly upon the lateral 

 line these have been depended on for the determination 

 of the " transverse rows of scales." Occasionally the 

 scale of a vertical row lies far enough above or below 

 the row of pores to be left out of the count, although the 

 row to which it belongs is continuous above and below 

 the line. This counting of the scales on the lateral line 

 instead of the vertical rows to which they belong has led 

 to confusion, because no two specimens of the same 

 species give similar results. 



It is an easy matter to arrange the species in a prob- 

 ably natural order; but, even with the fine series of grad- 

 uated characters described above, it has been impossible 

 to construct a " genealogical tree." The genus is prob- 

 a hi v a young and vigorous one; and extensive comparisons 

 of the young stages of the different species with the adult 

 condition, comparison of the different species with each 

 other at different ages, and a study of the later embry- 

 onic stages of these ovoviviparous fishes, together with the 

 few facts now known, would in a large measure solve the 



