378 



U. S. p. R. R EXr. AND SURVEYS — ZOOLOGY GENERAL REPORT. 



List of specimens. 



2. PETROMYZON CILIATUS, Ay res. 



Spec. Char. — Body sub-cylindrical, deeper than broad, caudal region very much compressed. Buccal disk sub-elliptical, 

 fringed upon its periphery. Head constituting about the tenth of the total length. Anterior dorsal fin lower than the second, 

 and separated from it by a space equal to the fifth of its length ; its origin being nearer the e.ttremity of the snout than the tip 

 of the caudal. Inferior lobe of caudal fin deeper than the upper. Color olivaceous brown, rather dark above and more 

 greenish beneath. 



Stk. — Pelromyzon ciliatus, Atres, in Cal. Acad. Nat. Sc. I, 1855, 44. 



Having before us a specimen twenty-four inches and a half in total length, labelled by Dr. 

 Ayres himself, tliere is no room to doubt as to species which we record in this paragraph. 



The body anterior to the dorsal fin is sub-cylindrical, deeper than broad, whilst it is com- 

 pressed posteriorly to it, becoming more and more so towards the caudal region, which is very 

 much compressed and quite thin. 



The liead is sub-conical, tapering anteriorly, and smaller than the chest. Measured from the 

 extremity of the snout to the first branchial orifice it forms about the tenth of the total length. 

 The buccal disk is of moderate development, sub-elliptical in shape, continuous all around ; its 

 periphery being provided with a series of small tentacles or fringes, with filiform tips and 

 somewliat flattened bases, inserted upon the black edge of the thickened lips. Immediately 

 within these fringes may be observed a continuous circular series of very small acute teeth, 

 from fifty-five to sixty in number, each surrounded by a little circular depression, with a raised 

 margin. When removed these teeth leave behind them small nipple-like papillae as the base 

 upon which they were inserted. Within these teeth or papillae, as the case may be, we observe 

 larger teeth. Seven rather small acute and conical ones occupy the anterior portion of the 

 buccal ellipsis, disposed upon two series — five belonging to the continuous series and two 

 forming an additional series in front ; four larger ones on either side, the two middle ones 

 tricuspid, the upper and lower pair being bicuspid ; eighteen very small, simple, conical, acute 

 teeth like the preceding row complete this series, standing in a circular depression like those 

 above alluded to. The buccal orifice, properly so called, is provided anteriorly with a tridentate 

 transverse piece, the middle tooth being considerably smaller than the lateral ones ; posteriorly 

 or inferifirly is another transverse piece armed with five teeth, the three middle ones being 

 somewhat smaller than the exterior two. At the entrance of the esophagus we observe three 

 elongated, finely serrated pieces, the uppermost two placed vertically, the inferior one hori- 

 zontally. The eyes are sub-elliptical ; the longitudinal diameter of the orbit entering about 

 eight times in the length of the side of the head from the first branchial orifice forwards 

 They are nearer the latter than the extremity of the snout. The seven branchial orifices are 

 vertically sub-elliptical, extending over a space somewhat longer than the cephalic region. 

 The structure of these orifices is quite complex ; they are surrounded interiorly by a smooth 



