DISCUSSION OF SPECIES AND THEIR DISTRIBUTION. "-'."> 



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 month. Eye moderately large, orbil elongate, near a vertical from the middle of the 

 length of the month, spiracle very small, over the hyomandibular; its distance behind the 

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

 ing as far back as the skull. Hoof and door of mouth covered with sharp scales, the 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) prominent above the floor of the mouth and free at its extremity about half an 

 inch, forming 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 cusps, 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 s\ m 

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

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

 with 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 six arches in order, 15, 14, 12, !t, <>, 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 tift h and sixth 

 extending back above the shoulder. 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 skull and, after receiving a branch from behind 

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

 in the tail, where it makes an abrupt turn downwards for about a quarter of an inch: under 

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

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

 the middle of the 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 coining into it near the end from the direction of the corner of the mouth. Pectorals 

 moderate, broad, rounded. Dorsal comparatively small, its posterior extremitj 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 

 to a vertical from the vent, a few of the anterior being horizontally flattened. Ventrals 

 large, broad, a little broader than long, rounded, posterior angle acute. Anal broad, long. 

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

 angle acute: produced into a filamentary point : margin very thin or membranaceous. Above 

 the muscular vertebral portion of the tail there is a narrow expanse of tin. widening back 

 ward, the edge of which is armed by a sharp series of chisel shaped 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 tin which descends is proved by the 

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

 tion of the tin is plainly indicated on the hinder margin of the tail about half \va\ down to 

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



