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 Tipper opening looking forward and a lower one looking backward, situated 

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

 to mouth. Eye modeiately large, orbit elongate, near a vertical from the middle oi' the 

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

 eye equal to tliat from eye to end of snout. Mouth cleft \'ery deep, sliglitly curved, t>xtend- 

 ing as far back as the skull. Roof and door of mouth covered with siiarp scales, the former 

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

 jaws about equal in length. Lips without a groove or labial fold. Glossoliyal cartilage 

 (basihyal) prominent above the iioor of the mouth and free at its extremity about half an 

 inch, forming a tongue. Teeth small, similar iu 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 tlie central. Bases of teeth broad, extending inward about the 

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

 next tooth, jjreveut the possibility of reversion or turning the cus^is forward. Fourteen 

 rows of teeth on each side on the upper jaws, no median series. A median row on tiie 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 (;eratohyal 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. Witlioutdissecting, twenty two brancliial 

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

 ceeding six arches in (»rder, 15, 14, 12, 9, (i, and 0, respei'tively. In mctst cases the outer 

 extremities of the i-ays arc produced in a sharp, fiexible point beyond the adjacent margin 

 of the gill covers. Gill openings very wide, oblique, the opposite series very narrowly se])a- 

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

 extending back above the shoulder. A broad opercular fiap covers the first l)rancliial apcr- 

 tui'c and is continuous and free across tlie isthmus, forming a frill or rufile; 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 ab(Uit as follows: Starting al)Ove 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 flank to the extreme end of the vertebral column 

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

 the chin on each side a line ruTis along the mandible and curving upwards disapj)ears 

 behind the angle of the mouth; a braiicli 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 upwai'd neai' tlie margin of the o))ercular flap, after receiving a sliort lirancli beliind the 

 angle of the mouth, continues to a point a very short distaiu'C behind tlie spiracle, small 

 branch coming into it near the end from the direction of the conierof themoutii. Pectorals 

 moderate, broad, rounded. Dorsal comparatively small, its postcricu- extremity extending 

 as far back as that of the aual, 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. Abo\(; 

 the muscular vertebral ])ortion of the tail there is a narrow exi)ansc of fin, 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 ab(Hit threesixtc^enths 

 of an inch in width. That it is the dorsal portion of the tin which descends is proxed by the 

 change in the direction of the jjoints of the scales and of the miu-us canal. The dorsal jior- 

 tion of the fin is plainly indicated on tlie hinder margin of the tail about half \v;iy down to 

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



