CLASSIFICATION OF THE CEPHALOCHORDA. 



285 



capense and B. calif orniense is very slight, and a com- 

 parison of the myotome formulae of the three species is 

 instructive. 

 B. elongatum — 



Total 79. 

 B. capense — 



Total 75. 

 B. calif orniense 

 Total 69-73. 



Formula 49, 18, 12. 



Length 39-60 mm. 

 Length 39-48 mm. 



Length 74 mm. 



Formula 47, 19, 9. 

 (44, 16, 9 

 Formula \ 45, 17, 9 

 (44, 19, 8 



It will be seen from this that they are very closely 

 related. They agree in all other respects, and while the 

 formulae of B. calif orniense approach those of B. elongatum, 

 the last formula given agrees very closely with that of 

 B. capense. 



We may reasonably doubt the separate specific identity 

 of these three forms. Only the examination of a large 

 collection of each will really settle the point. All three 

 are little known forms, and in the end will probably be 

 found to be varieties of one species. B. indicum agrees 

 with B. calif orniense. in all but two characters, (1) the 

 arrangement of the myotomes, and (2) the characters of 

 the pre-oral lobes. The total number of myotomes in 

 each is the same, 69-73, but the arrangement differs, as 

 the following table shows. 

 B. indicum— 



69 Tattersall. 

 71 Willey. 

 - 70 Tattersall. 



41, 14, 14 



42, 14, 15 



43, 14, 13 



B calijorniense — 

 f 44, 16, 9 

 45, 17, 9 



44, 19, 8 



69 Cooper (J. G. 

 71 Kirkaldy. 

 71 Kirkaldy. 



