1911] Michael: ChactognatJia of the San Diego Region. 



23 



Primarily this depends upon degree of transparency of the 

 species. Doncaster (1902b) has represented this appearance, 

 but his drawings lack accuracy of measurement, which renders 

 them useless for purposes of identification. Most authors, how- 

 ever, have published merely outline drawings and, while accu- 

 rate in measurements, they do not suggest the distinctive appear- 

 ance of the species. To make this paper more serviceable to 

 those unacquainted with the group I have endeavored to com- 

 bine the merits of Doncaster 's (1902b) drawings with accuracy 

 of measurement. 



Krumbach (1903) has discovered characters of much taxo- 

 nomic value in the minute anatomy of the seizing jaws, and I 

 have endeavored to extend his descriptions to the San Diego 

 species. This author's contribution merits more attention than 

 it has received, for these hard structures offer the only means of 

 identification applicable to poorly preserved material. It is 

 well to note, hoM-ever, that to recognize these distinctive char- 

 acters requires the most delicate microscopic manipulation. 



In measuring the curvature of the seizing jaws the follow- 

 ing method has been employed. A camera drawing (text fig. 1) 



was first made. A per- 

 pendicular, ah, was then 

 erected upon the edge 

 of the jaw at the junc- 

 tion of the shaft, sh, 

 with the ventral column, 

 vent. col. A second line, 

 cd, was then drawn 

 tangential to the point, 

 pt. The proportion ah/ 

 cd indicates the extent 

 of the curvature. 



In preparing the ta- 

 bles of diagnostic mea- 

 s u r e m e n t s for each 

 species only the most 

 perfectly preserved ma- 

 terial has been used. In 



