" 3. The total length is the distance between the end of the snout 

 and the extremity of the caudal fin, tvhen stretched out. 



" 4. The last dorsal and anal ray is, generally, bifid to the base : it 

 is counted as one, because only one intemeural and interhgemal spine 

 corresponds to it. 



" 5. L. lat. gives the niunber of pierced scales constituting the 

 lateral hue from the humeral arch to the root of the caudal fin, i. e. 

 the number of transverse series cf scales covering the body between 

 the points mentioned. The scales of the lateral line are often 

 smaller or larger, or irregular, and not congruent with the transverse 

 series ; in these cases I have counted the transverse series. 



" 6. L. transv. gives the number of scales in a series, which runs 

 from the origin of the dorsal fin obliquely downwards to the median 

 line of the abdomen, crossing the lateral line. It indicates the 

 number of longitudinal series of scales between the origin of the 

 dorsal fin and the lateral line, and between this and the abdomen. 

 Sometimes the transverse line has such an oblique direction that the 

 number of its scales would be greater than that of the longitudinal 

 series : in this case I count the latter. — TJie numbers of the lateral 

 and transverse lines are of sjieciflc value. 



" 7. The statement of the size of the eye, relative to the length of 

 the head and its parts, is to be applied cautiously, this organ being 

 comparatively much larger in young specimens than in mature ones. 

 Statements taken from mature specimens of different species, of course 

 have every right to be received into the diagnosis. 



" 8. In the descriptions of the skeleton the terminology given by 

 Prof. Owen has been used. 



" 9. In the statement of the length of the vertebral column, the 

 centrum only of the last caudal vertebra is included. 



" The Plates i-eferred to, and executed bj' Mr. Ford, A\ill be pub- 

 lished as a separate volume." 



JOHN EDWARD GRAY. 



British Museum, 

 May 5, 1859. 



