DISCUSSION OF SPECIES AND THEIR DISTRIBUTION. 23 



angled or shovel- shaped at the top. Nostril moderate, vertical, separated by a fold from 

 each side into an upper opening looking forward and a lower one looking backward, situated 

 about midway from eye to end of snout and near the middle of the space from top of head 

 to mouth. Eye moderately large, orbit elongate, near a vertical from the middle of the 

 lengtli of the mouth. Spiracle very small, over the hyomandibular; its distance behind the 

 eye equal to that from eye to end of snout. Mouth cleft very deep, slightly curved, extend- 

 ing as far back as tlie skull. Roof and floor of mouth covered with sliarp scales, tlie former 

 curving upward very strongly behind the teeth between the nostrils. Upper and lower 

 Jaws about equal in length. Lips without a groove or labial fold. Glossohyal cartilage 

 (basihyal) xirominent above the floor of tlie mouth and free at its extremity about half an 

 inch, foi'ming a tongue. Teeth small, similar in both jaws, several in each row in function 

 at the same time, each with three long, smooth, curved, backward directed, slender, very 

 sharp casps, each of which bears some resemblance to a serpent's tooth. A small cusp on 

 the base at each side of the central. Bases of teeth broad, extending inward about the 

 length of the cusps, terminating in two prongs which, extending beneath the base of the 

 next tooth, prevent the possibility of reversion or turning the cusps forward. Fourteen 

 rows of teeth on each side on the upper jaws, no median series. A median row on the sym- 

 physis of the lower jaws, its teeth similar in size and shape to those of the thirteen rows on 

 each side of it. Hyomandibular and ceratohyal closely and somewhat firmly connected 

 witli the jaws at the hinge or hinder angle of the latter. Branchial arches long, very slen- 

 der, with sharp small scales on their inner edges. Without dissecting, twenty-two branchial 

 rays can be counted on the hyomandibular and ceratohyal (the first arch) and on the suc- 

 ceeding sis arches in order, 15, 1-1, 12, 9, 6, and 0, respectively. In most cases the outer 

 extremities of the rays are produced in a sharp, flexible point beyond the adjacent margin 

 of the gill covers. Gill openings very wide, oblique, the opposite series very narrowly sepa- 

 rated on the throat, the fourth in front of a vertical from the pectoral and the fifth and sixtli 

 extending back above the slnmlder. A broad opercular flap covers the first branchial aper- 

 ture and is continuous and free across the isthmus, forming a frill or ruffle; it is held in 

 place and prevented from turning forward by a thin fold or wall of membrane, nearly an inch 

 in height, attached immediately beneath the middle of the basihyal. The external distri- 

 bution of slime canals is about as follows: Starting above the nostril in front of the eye, a 

 line turns backward along each side of the skall and, after receiving a branch from behind 

 the eye, continues along the middle of each flank to the extreme end of the vertebral column 

 in the tail, where it makes an abrupt turn downwards for about a ([uarter of an incli; under 

 the chin on each side a line runs along the mandible and curving upwards disappears 

 behind ihe angle of the mouth; a branch of this, beginning nearly on a vertical beneath 

 the middle of tlie space between the eye and nostril, runs farther from the mouth and turn- 

 ing upward near the margin of the opercular flap, after receiving a short branch behind the 

 angle of the mouth, continues to a point a very short distance behind the spiracle, small 

 branch coming intoit near the end from the direction of the corner of the mouth. Pectorals 

 moderate, broad, rounded. Dorsal comparatively small, its posterior extremity extending 

 as far back as that of the anal, angle blunt. The upper margin of the dorsal is armed with 

 a series of enlarged, compressed, chisel-shaped scales, which extends forward on the back 

 t<i a vertical from the vent, a few of the anterior being hoi-izontally flattened. Veiitrals 

 large, broad, a little broader than long, nmnded, posterior angle acute. .Vnal broad, long, 

 rounded, aeute-angled posteriorly. Caudal long, very broad, rounded anteriorly, posterior 

 angle acute; produced into a filamentary point ; margin very thin or membranaceims. Above 

 the muscular vertebral i)ortion of the tail there is a narrow expanse of fin. widening back- 

 ward, the edge of which is armed by a sharp series of chisel -sliaped scales, and extended 

 downward behind the end of the vertebral column, where it becomes about three-sixteenths 

 of an inch in width. That it is the dorsal portion of the fin which descen<Is is proved by the 

 change in the direction of the iroints of the scales and of the mucus canal. The dorsal por- 

 tion of the fin is plainly indicated on the hinder margin of the tail about halfway down to 

 the filamentary point. The chisel-shaped scales are in reality formed from two series (one 



