2 20 Alexander W. Evans, 



According to Leitgeb the scales in certain species, such as 

 M. domingensis and M. nitida, are all of the median type while 

 in M. chenopoda the laminar scales are less numerous than the 

 median scales and the marginal scales are absent altogether. In 

 Goebel's figure of M. chenopoda^^ a single laminar scale is shown 

 among sixteen median scales and the implication is made that the 

 number of laminar scales is very small. The writer has exam- 

 ined numerous specimens of M. paleacea (which includes M. 

 nitida), of M. chenopoda and of other species and finds laminar 

 scales always present (see Fig. 6, H-O). They differ from the 

 laminar scales in M. polymorpha, however, in being situated 

 much closer to the median scales. On account of their shorter 

 lines of attachment they extend only a small part of the 

 distance toward the median line. The laminar scales usually 

 alternate with the median scales but occasionally there may 

 be two laminar scales between two successive median scales. 

 Under these circimistances one of the laminar scales is often 

 reduced in size. 



The species just noted will give some idea of the differences in 

 arrangement which the ventral scales may show. These dif- 

 ferences can often be utilized in separating species, but the best 

 differential characters yielded by the scales are those drawn from 

 the appendages. These are, with very rare exceptions, borne 

 singly and, as has been shown, are confined to the median scales. 

 Although the appendages vary, within wide limits in certain 

 species, they nevertheless present striking and distinctive features. 

 In comparing them the form, the character of the margin and 

 apex, the size of the cells, and the presence or absence of cells 

 containing oil-bodies should be taken into consideration. With 

 respect to size the cells may be approximately the same through- 

 out the entire extent of an appendage (see Fig. i6, F, G). It 

 is much more usual, however, for the median cells to be much 

 larger than the marginal cells and the gradation from one 

 to the other may be either gradual (see Fig. 7) or very abrupt 

 (see Fig. 5, A-D). The texture of the scales, aside from 

 the appendages, is much the same throughout the genus. The 

 scales and their appendages will be again considered in connection 

 with the various species discussed below. 



