296 E. C. STARRS. 



The dentary is a strong bone and so closely attached to the 

 articular that there is no play between them as is usual in other 

 forms. 



The angular is a very small nodule of bone on the inner sur- 

 face of the articular, entirely hidden when the skull is viewed lat- 

 erally. The interopercle is attached to the angular by a ligament. 



The opercle, preopercle and subopercle together form an isos- 

 celes triangle with its greatest length extending backwards. The 

 subopercle forms the posterior point of the triangle, and is inter- 

 posed between the points of the opercle and preopercle. The 

 preopercle is developed backward from its articulation with the 

 hyomandibular to a long point, forming-nearly the entire lower 

 border of the opercular system. It forces itself between and 

 entirely separates the subopercle and interopercle, bringing the 

 opercle entirely above it. Its anterior end extends forward in a 

 long point behind the quadrate nearly to the mandibular con- 

 dyle. The interopercle is a small triangular bone, lying free 

 behind the quadrate and hidden from sight by that bone when 

 the skull is viewed laterally. It is unconnected except by a liga- 

 ment to the angular. There is a low ridge running along the 

 lower edge of the opercle, and a very high sharp one running 

 along the lower edge of the preopercle and the quadrate nearly 

 to the condyle of the mandible. 



A broad membranous preorbital plate is all that remains of the 

 suborbital chain of membrane bones. It bears a sensory tube 

 which opens anteriorly to the exterior through a small pore a 

 couple of millimeters in front of the anterior nostril. The tube 

 crosses the plate obliquely downward and backward, forking 

 widely in front of the eye, and opening to the exterior at the 

 lower edge of the plate through two widely separated pores. 

 These pores appear in the skin at the upper border of the mouth 

 6 or 7 mm. apart. 1 A third pore 4 mm. anterior to these, and 

 near the front of the mouth, forms the exit of the sensory tube 

 traversing the nasal plate. 2 At the place the preorbital tube 

 forks the plate is slightly ossified. 



1 The specimen described is I cm. in length. 



2 It appears probable that the suborbital sensory tube is never present in the 

 Teleosts unossitied. There may be a series of pores or nerve hillocks, as in Porich- 

 thys, but they do not open into a continuous tube. I have examined a" large number 

 of forms known to have no suborbital bones, but find no tube present in any of them. 



