312 LAKE SUPERIOR. 



margin of the orbits, and touches the preoperculum only hy its 

 lower margin. The rest of the cheek, between the eye and the pre- 

 operculum, remains completely bare. They are finely granulated, 

 without spines or denticulations, though their outer circumference 

 presents a few notches. The preoperculum borders the posterior 

 and lower margins of the cheek in the form of an obtuse angle, 

 dilated on the summit, and narrow at its margins. The operculum 

 is triangular with slightly concave sides, the posterior margin round- 

 ed, and the surface radiately striated. The suboperculum forms an 

 acute angle ; its anterior branch is convex on the side of the oper- 

 culum, and concave on the side of the interoperculum, which has 

 the form of a small sub rectangular triangle. 



There are about three equal branchiostegal rays. The branchial 

 fissure itself is well proportioned. The suprascapular and scapular 

 bones are not visible externally ; they attach the humeral to the skull. 

 The upper extremity of the humeral forms a small triangle, with granu- 

 lar surface, one side of which extends above the base of the pectorals, 

 thus bounding, at the upper part, the large smooth space which sepa- 

 rates these latter from the branchial opening. This smooth space is 

 bordered on its lower circumference by the narrow prolongation of 

 the cul)itus on each side, which, at the lower part of the body, forms 

 a triangle, whose summit advances like the point of a gothic arch in the 

 isthmus near to the branchial fissure. The sides extend parallel as 

 far as the ossa innominata, without uniting with them. They thus 

 circumscribe a bare triangular space in the enclosure of the arch, 

 which embraces not quite half of the space, it being a parallelogram 

 for the rest of its extent. The shield under the belly formed by the 

 ossa innominata is triangular, and the basis turned forwards is stri- 

 ated transversely at the outer margin, from which is cut a segment 

 of a circle, which is sometimes obtusely triangular where the bare 

 space disappears, which the branches of the cubitus circumscribe, as 

 we have just mentioned. The hinder point of the triangle is obtuse, 

 and terminates at some distance from the anus. The ventral spine 

 does not quite reach the extremity of the triangle. The ascending 

 branch of the ossa innominata rises at a small distance from the pec- 

 torals, inclining backwards. It is somewhat more dilated at its sum- 

 mit than at its origin, forming thus an elongated isosceles triangle, 



