NOTES ON THE IDENTIFICATION OF CH/ETOGNATHA. 75 



elongated wedge. Old jaws are supplied with a pronounced 

 crest. 



Kroluiia liainata (lo). 



Jaws heavy with broad oval cross-section. Pulp/ only scantily 

 fills the center of the canal can. Pulp swollen .yrcas in 6". niiiiiina. 

 Base of point b and top of shaft / converge toward the edge of 

 the shaft eg. 



Taken in connection with the seizing jaws the teeth afford an 

 excellent means of identification. Their arrangement into two 

 pairs of rows distinguishes Spadella and Sagitta from Krohnia, 

 which has but one. Within the genus Sagitta a glance at the 

 table at the close of this paper will indicate the importance of 

 mere number. It is advisable that the limits of variation for 

 every length of individual be accurately known. Were this ac- 

 complished, by combining the number of anterior and posterior 

 teeth with the length of individual, a criterion of identification 

 would result of much value to the systematist. 



The form and arrangement of the teeth, if properly recorded, 

 will considerably assist in identification. Some teeth are slender, 

 some broad, so that proportional measurements of width and 

 length are desirable ; the length of tooth should also be com- 

 pared to the length of individual so as to define exactly what is 

 meant by saying that the posterior teeth of Sagitta licxaptcra are 

 long and slender, while those of ^. ferox are long and broad. 

 In any group like the Chaetognatha, where, at best, identification 

 is difficult, we should endeavor to rid ourselves of characters 

 based upon mere comparisons. All such characters may, at the 

 expense of a little labor, be reduced to exact or proportional 

 measurements. If one merely says that the posterior teeth of 

 Sagitta siboga "are long, broader, and with narrower bases than 

 in bedotiy anyone attempting to identify a 6". siboga would won- 

 der whether the teeth were absolutely broader, broader in pro- 

 portion to the length of tooth, or broader in proportion to the 

 length of individual. 



The inclination of the teeth, whether upright, externally or 

 internally oblique ; the proximity of setting, whether close or 

 distant, are of some importance. Fowler ('05, '06) has used 



