CLASSIFICATION OF THE CEPHALOCHOKDA. 281 



From this table it is apparent that the closest affinity 

 exists between these three supposed species. The differ- 

 ences are trivial, especially those of the fins, which, 

 besides varying so much in one species, are so delicate 

 that only in the best preserved material do they retain 

 their true shape. The differences between the three 

 forms as shown above are not sufficient to separate them 

 specifically. It is quite evident that they have been 

 separated merely on the arrangement of the myotomes. 

 The number of myotomes in B. caribbceum is 59 to 61 ; in 

 B. laneeolatum 58 to 62, and in B. belcheri 62 to 66. It will 

 be seen that the total number of myotomes in B. caribbceum 

 is the same as that of B. laneeolatum, the former total 

 falling within the limits of the latter; while the total 

 number of myotomes in B. belcheri never exceeds that of 

 B. laneeolatum by more than three. In Asymmetron 

 bassanum the range allowed is 70 to 78, a range of 8, yet 

 in a similar range here, 58-66, three species are distin- 

 guished — an obvious inconsistency, especially when the 

 similarity of the other characters is considered. Nor do 

 the arrangements of the myotomes differ so markedly as 

 to justify a separation. The average arrangement in 

 B. caribbceum is 37, 14, 9 ; in B. laneeolatum 36, 14, 12, and 

 in B. belcheri 38, 17, 9. The difference between B. 

 laneeolatum and B. belcheri may appear great, but the 

 following table, compiled from the observations of 

 different workers, shows how the characters of one species 

 fade gradually into those of the others, so that it is 

 extremely difficult to decide where to draw the line 

 between them. 



