152 University of California Publications in Zoology [Vol. 13 



These are distributed over the roof and floor of the buccal cavity, the 

 general distribution above and below being somewhat similar. Above, 

 the denticles form a more or less compact pavement, especially in the 

 anterior part of the roof; they extend back to a line connecting the 

 spiracles, behind which they rapidly thin out, so that in the pharynx 

 the denticles are confined largely to the visceral arches. 



Both above and below the individual stomodeal denticles may take 

 irregular positions around sense-buds in the pattern (see pi. 8, fig. 1). 

 In some cases this irregularity above expresses itself in a plan by 

 which the spine, which normally points posteriorly, points towards or 

 away from the middle line or even anteriorly. The same grouping 

 may occur below where the spine normally points anteriorly. 



The form of these denticles, while often imperfect, is essentially 

 similar to that of the scales which we have already described as ventral 

 in type. In general there is an anterior arm which, however, seldom 

 possesses the characteristic wedge-shaped groove. The lateral wings 

 are relatively very broad, and in some cases the spine becomes trun- 

 cated by a cupping upward of the tip, thus making the surface of the 

 scale concave. In this latter modification crests may sometimes be 

 seen to extend from the lateral arms to the blunted tip of the spine. 



Scales located under the pectoral fin are also modifications of the 

 ventral type. Plate 8, figure 4, represents a strip of integument with 

 types of scales extending from the ventral over the anterior margin 

 to the dorsal side of the fin. In this three general areas are seen, the 

 first of which is uppermost in the figure and is covered by the modified 

 ventrals now under consideration. These scales, though spade-shaped, 

 are especially thick and heavy. The spine is depressed and the angles 

 between it and the lateral arms are almost straight. The wedge- 

 shaped groove, characteristic of the heterodont scale, is here often 

 absent or represented only by a shallow groove. 



The second and third areas of this strip may be briefly mentioned 

 here. The scales of the second area, which in the figure occupies the 

 middle region, are so closely packed together as to form a compact 

 pavement on the margin of the fin. It will be noted, however, that 

 these scales are anteriorly, not ventrally, placed, and that from their 

 outline it would be difficult, at this time, to characterize them as 

 modifications of any particular type. The third area in this figure, 

 the one most ventrally located, is composed of scales of more clearly 

 differentiated form ; these are located on the dorsal side of the fin and 

 constitute the dorsal type of scale. 



