III. COTTOIDS OF NORTH AMERICA. 39 



ology of the United States Exploring Expedition. There will also appear the 

 figure of our Cottopsis, the greatest iconographic desideratum of this Monograph. 



3. SPECIES WITH FOUR SOFT BAYS TO THE VEXTRALS. 



I. COTTUS RICIIARDSONII, AGASS. 

 PLATE I. Figs. 1 and 2. 



Sjn. Coitus RicharJsonii, AOASS. Lake Sup., 1850, p. 300. GIRARD, Proc. Am. Ass. Adv. Sc., 1850, 

 p. 410; and, Proc. Boat. Soc. Nat. Hist. III., 1850, p. 189. 



The largest specimens of Cottus which we have seen, belong to this species; they 

 are four inches and three-quarters in total length, the caudal fin included. 



The general form of the body is elongated, quite regular. Its greatest depth 

 taken behind the pectorals is contained nearly six times in the length ; and its least 

 depth, in advance of the caudal, a little more than seventeen times. The decrease 

 is uniform and gradual from the head backwards. The thickness is a little less 

 than the depth. The free space between the second dorsal and the caudal is equal 

 to two-thirds of the depth on the peduncle of the tail. 



The head is very much depressed, subconcave above, and forming about the 

 third of the length of the fish, the caudal fin excluded. Its width is equal to the 

 three-fourths of its length, whilst its depth is a little more than the half of the 

 latter. The mouth is large and wide, its amplitude measuring three-quarters of an 

 inch ; its angles reach a vertical which would pass through the pupil. The jaws 

 are of equal length, beset with a band of very minute teeth, the summit of which 

 is curved inwards. The lips which line the jaws are capable of great extension, 

 from the branch of the dentary and premaxillaries unto the angles of the mouth; 

 whilst on the symphysis of these bones they are reduced to a mere cutaneous ridge. 

 The eyes are of medium size, circular, and nearer to the end of the snout than to 

 the posterior edge of the opercular by one of their diameters, Avhich is contained five 

 times and a half in the length of the head. The interorbital space above is equal to 

 one of the said diameter, the distance being measured from the visual rims ; for the 

 bony arcade is much narrower, as seen in Fig. 18, Plate III., which represents an 

 upper view of the skull of this species. The anterior nostrils, situated nearly 

 midway between the anterior rim of the eyes and the end of the snout, opens 

 exteriorly through a membranous tube which rises above the surface of the skin. 

 The posterior one is nearer to the eye, and situated on a line below the anterior 

 one. The preopercular spine is very stout at its base, very acute at its extremity, 

 and suddenly curved upwards. The subopercular spine is quite conspicuous, 

 although generally concealed under the skin. The posterior and upper extremity 

 of the opercular terminates in a flat and sharp process concealed within the thick- 

 ness of the membrane which lines the edge of that bone, whence it passes also 

 along the inferior edge of the subopercular. The branchiostegals, six on each 

 side, are slender and cylindrical. The isthmus, under the throat, is three-eighths 

 of an inch wide. 



