NOTES ON THE IDENTIFICATION OF CH.-ETOGNATHA. 8 1 



Key for the Determination of the Species of Spadella. 



1. Average width of collarette nearly half that of the body, widest slightly anterior 



to the tail septum. Length of fin always less than 5 times its width. An- 

 terior teeth 7 to 10. Posterior teeth il to 16 Spadella draco. 



2. Average width of collarette much less than half that of the body ; widest slightly 



posterior to the head. Length of fin always more than 5 times its width. An 

 terior teeth 3 to 5. Posterior teeth 3 to 4 Spadella cephaloptera. 



Description of Table. 



The data for this table have been gathered from various 

 sources, but mostly from the investigations of Fowler ('05, '06) 

 and Krumbach ('03). In proportional measurements, number of 

 seizing jaws, and number of teeth, the extremes of variation have 

 been indicated wherever possible. 



In the case of Sagitta ivJiartoni the data have been obtained 

 from Fowler's " Contributions to our Knowledge of the Plankton 

 of the Faroe Channel," 1896. In this instance a considerable 

 discrepancy, due in all probability to a typographical error, is 

 found in comparing the drawing with the descriptive measurements. 

 From Fowler's description the width of the anterior fin varies 

 from 10 to 15 per cent, of the total length ; from his drawing it 

 measures but 2.8 per cent, of the total length. Similarly, in the 

 width of the posterior fin, his measurements show variation from 

 13 to 21 per cent, of the total length, while his drawing shows it 

 but 5.7 per cent. In no other species has the width of the ante- 

 rior fin been over 6 per cent, of the total length, nor the width 

 of the posterior fin over 7 per cent. For this reason I have 

 utilized the fin measurements as taken from the drawing rather 

 than from the description of Sagitta %vharto)n. 



I desire to express my obligations to Dr. C. A. Kofoid, 

 through whose direction, advice, and criticism I have received in- 

 valuable aid. 



Zoological Laboratory, 



University of California, 

 Berkeley, April 27, 1908. 



