322 



BULLETIN OF THE BUREAU OF FISHERIES 



Pyloric caeca 



The number of pyloric appendages is rather variable within the species, but the 

 averages show interesting differences in a few cases. They are counted below chiefly 

 for specimens from Lake Huron. 



Species 



Leucichthys: 



johannae 



alpenae 



zenithicus_. 

 reighardi 

 nigripinnis- 

 kiyi-_ 



Number 

 of speci- 

 mens 



Range 



142-222 

 126-181 

 92-150 



115- 142 

 132-194 



116- 167 



Species 



Leucichthys — Continued. 



hoyi__- 



artedi 



nipigon 2 



Coregonus elupeaformis 



Prosopium quadrilaterale.. 



Number 

 of speci- 

 mens 



Range 



88-164 

 109-165 

 109-145 

 208-264 



87-117 



'Lake Michigan specimens. 



2 Lake Nipigon specimens. 



It appears that in Leucichthys hoyi and zenithicus have, on the average, the 

 fewest caeca, while johannae has the most. The ranges of the former overlap that of 

 the latter, and more counts probably will show that overlapping occurs to a greater 

 extent than appears in the table. Coregonus has, on the average, more caeca than 

 either Leucichthys or Prosopium and thereby is differentiated sharply from the 

 latter, which has fewer caeca than most Leucichthys. It is possible that this character 

 is influenced by nutrition. 



Head Form 



The head in all forms presents four surfaces — a dorsal, a ventral, and two lateral. 

 The dorsal surface is bounded approximately by a line running from the articulation 

 of the maxillary caudad along the dorsal edge of the orbit, and the ventral by a line 

 running caudad along the inner edge of the dentary. 



In Leucichthys the dorsal surface has the form of a trapezoid with two equal 

 sides, due to the shape and position of the premaxillaries, and is more or less convex 

 from side to side, the degree of convexity becoming greatest in the region of the 

 occiput. A faint carina, which becomes more conspicuous on drying, runs through 

 its length. The lateral surfaces are nearly flat and converge distinctly in a down- 

 ward direction. In shape they are roughly triangular, depending again on the shape 

 and position of the premaxillaries. In alpense the apex is rather rounded, in reighardi 

 truncated, and in the rest rather acute or obtuse as the angle made by the premaxil- 

 laries with the body axis becomes greater than 45°. The ventral surface, like the 

 dorsal, is convex and corresponds to it in shape. 



The depth and width of the head is greatest in artedi and nigripinnis. The 

 depth is least in reighardi and zenithicus. The proportion of the head length to that 

 of the whole fish, expressed by L/H, is but slightly different for the forms of this group 

 and therefore has little systematic value. (See Table 8.) Its significance is reduced 

 further by the fact that it changes with the growth of the individual. The races of 

 artedi, however, tend to have proportionally the shortest heads among the forms of 

 Leucichthys. 



The relative head length varies within the species, often to a conspicuous extent. 

 Making allowance for difference in size between the groups of individuals compared, 

 it seems that in johannse and alpense the head is somewhat larger in Huron; in 



