300 Description of the Argiilus Catostomi. 



de, d'e', which near the center of the sides of the oval mass (at e) 

 curving suddenly inward and downward and at the same time enlarg- 

 ing tends to the base of the maxillae. This bone at its angle e forms 

 an ear-like projection to the oval mass. On each side of the center 

 arises a curved, corneous and slightly colored maxilla {f;f'- figs. 

 4 and 5,) which extends forward beneath and beyond the arch; the 

 broad inner edge of each is serrated. An indistinct line near the apex 

 appears to separate a short apical joint. These maxillae approach 

 at their extremities and are each connected at their base with one 

 of the forks of a long, narrow, furcated bone g, which extends out- 

 ward and as far forward as the attachment of the sucker sheath to 

 the body, where it appears to be loosely connected with the sur- 

 rounding muscles. The other fork of this bone is connected with 

 the lateral bones before described as tending towards the base of the 

 maxillae after forming an ear-like projection. Between and con- 

 nected with the maxillae near their base, are two horizontal united 

 processes, (A, Fig. 5,) which become visible on the retraction of the 



The maxillae are capable of a slight motion back and forth in con- 

 nection with the ear-like projections, which is effected by means of 

 muscles extended nearly in the direction of the bones just described, 

 and inserted near the anterior part of the base of the suction feet. 



Between the two maxillae laterally, the bony arch above, and the 

 lip below, appears the orifice of the mouth, (above h, Fig. 4.) Be- 

 yond the maxillae is frequently observed an internal longitudinal 

 fissure, the opening of which is always accompanied with a retraction 

 of the lower lip. On withdrawing this lip, and forcibly severing 

 and uplifting the bony arch with the membranes, and the maxillae 

 with the long narrow bones to which they are attached, a second set 

 of organs, similar to the first, presents itself. The maxillae of the 

 inner mouth, which may, for distinction, be called the inner maxilla, 

 are in shape, situation and structure, like the outer. They are dimly 

 seen from without, just in front of the external maxillae, (Fig. 4.) 

 The longitudinal fissure above described appears to be situated in the 

 upper membranes connected with the inner mouth, and extends for- 

 ward from the bony arch of the inner mouth between the maxillae. 

 In endeavoring to trace analogies between this mouth apparatus and 

 that of the more highly organized Crustacea, we are led to believe 

 that the sheath of the sucker represents the labium, which may be 

 supposed to be greatly elongated, and by the union of its lateral 



