NOTES ON THE IDENTIFICATION OF CH/ETOGNATHA. /I 



mination. The comparative size of the head would seem to be 

 due to the extent to which contraction occurs at death ; if the 

 contraction be sh'ght the head appears larger, if great it appears 

 smaller. This also applies to a less extent to the presence or 

 not of a neck but, allowing for the variation thus produced, it 

 may have some taxonomic significance. Again, the presence or 

 absence of color seems to vary with the individual rather than 

 with the species. Fowler ('05) has obtained, in the same haul, 

 individuals of the same species, some a salmon pink, and others 

 without color. The shape of the fins, whether triangular or half 

 elliptical, would be an excellent character were the fins not so 

 frequently damaged. Fowler ('05) has obtained specimens with 

 a triangular fin on one side which had been rubbed into an 

 ellipse on the other. One is often still less certain, from evidence 

 derived from preserved material, whether the tail fin is truncate or 

 rounded in nature. 



The structural features then, which are available for diagnosis, 

 consist of the cephalic armature, musculature, lateral fields, 

 corona ciliata, and proportional measurements of various regions 

 of the body. The table, at the close of this paper, includes all 

 valid toxonomic characters, a discussion of which follows. 



Prior to Krumbach's ('03) paper on " Die Greifhaken der 

 Chaetognathen " practically the only use made, in classification, 

 of the seizing jaws consisted of their enumeration and, even so, 

 the tendency has been to describe the species on a basis of one 

 or two individuals so that not enough latitude has been left for' 

 variation within the species. The number of seizing jaws is a 

 very important matter and should be tabulated, together with 

 the number of teeth and length of specimen, for a considerable 

 number of individuals. When the number of seizing jaws is 

 combined with their anatomical characters, as elaborated by 

 Krumbach ('03), they present excellent criteria for identification, 

 and, in many, cases, where preservation is poor, practically the 

 only safe criteria. Krumbach ('03) has defined the differences 

 among the various species in the form and curvature of the 

 seizing jaws, the presence and extent of a crest along the shaft, 

 presence and nature of serrations, curvature and shape of the 

 points, extent to which the point is inserted into the shaft, extent 



