PHARYNGEAL TEETH OF FISHES. 



457 



group. The lower pharyngeal bones are united, and carry a 

 group of pavement-like teeth; at the back and in the middle 

 they are of large size and show marks of grinding action; on the 

 outer sides of the middle ones and coming towards the apex 

 of the triangle are smaller conical teeth (fig. I., 2). 



Ditrema temminckii, a fish from Tokyo, Japan, has twelve 

 long horny gill-rakers with small bristles on their inside edge ; 

 three are rudimentary ones, all on the cerato-hypo portion of the 

 first branchial arch with six on the epibranchial. The length of 



Neoditrema ransonettii. 



Fig. I. 

 Ditrema. temminckii. 



Hysterocarpus traski. 



the longest one equals the depth of the gill-laminae below it. 

 The other arches have tubercle gill-rakers fitting closely and 

 making a good filter. The upper pharyngeal teeth consist of a 

 small row of soft bristles on the head of the second epibranchial, 

 and a roughly circular plate of strong conical teeth set closely 

 together on the heads of the third and fourth epibranchials. The 

 lower pharyngeal bones are united and carry a triangular group 

 of conical teeth set very closely together, small at the front apex 

 and getting larger posteriorly, the last row being comparatively 

 large (fig. I., 3). 



(To be continued.) 



ZooL 4th ser, vol, XIX.. December, 1915, 



