2 BULLETIN 10 0, UNITED STATES NATIONAL MUSEUM 



I have followed as nearly as possible the sequence of characters 

 as given in my preceding volumes, so that the whole series will be 

 uniform. This is a little at variance with the method used by most 

 ichthyologists in describing either elasmobranchs or chimaeras. Thus 

 the depth of the body refers to the greatest body depth and the 

 number of times it is contained in the body to the beginning of the 

 lower caudal lobe, or subcaudal as it is usually termed with reference 

 to sharks and rays. The head is measured from the snout tip to 

 the first gill opening, with the same proportions, its width, in the 

 case of sharks, referring to its length. Likewise the snout, measured 

 from its tip to the eye, the eye, the mouth width, and the interorhital 

 are all given with reference to the head. The space between the 

 snout tip and the mouth is the preoral length. The space between 

 the nostrils is the intem^rial. In the scale structure in the case of 

 sharks it is quite varied and is given from microscopic examination. 

 The fins, when present, as the dorsals and anal, are given with refer- 

 ence to their length in comparison with the head. The caudal is 

 often very variable, sometimes longer than the rest of the body and 

 usually with a well-developed lower lobe or subcaudal. In the ray- 

 like forms the pectorals gradually widen until the body contour is a 

 variable wide disk, often much wider than long. Its length is thus 

 measured from the snout tip, or end, to the hind edges of the pectorals. 



"With respect to the bony fishes included, as the herrings, anchovies, 

 catfishes, and carps, the same method of description is used. If the 

 lower jaw should protrude in front, the snout length is given with 

 the number of times it is contained in the head, followed by the 

 phrase "from snout tip," this showing that the lower jaw is not 

 included in the measurement. Thus the same dimensions for the 

 head are intended to follow through the description, or imtil it is 

 said to be the total length of the head. The gill rakers are counted 

 on the first arch, those above or below being indicated by the plus 

 sign, the former mentioned first. 



The scales of bony fishes are counted in the lateral line to the 

 caudal base or hypural bone, and such as may occur on the caudal 

 base are so mentioned. If no lateral line is present the count is made 

 in a similar location or axially along the side of the body. The ab- 

 dominal scutes are given with a plus sign to indicate those that pre- 

 cede and those that follow the ventral fins. In indicating fin spines 

 roman capitals are used, and simple or rudimentary rays are shown 

 by means of small capitals. 



As in preceding volumes acknowledgements are made to Dr. Hugh 

 M. Smith and those of the scientific corps engaged in the work of 

 the expedition. I wish also to acknowledge my indebtedness to 



