— 136 — 



moid, tlie recesses of opposite sides being separated by a thin wall of bone. The mesethmoid extends 

 entirely through the antorbital cartilage, and presents, on the ventral surface of that cartilage, a median 

 circular surface which lies directly upon the parasphenoid; the vacuity found in this part of the bone 

 of T. hirundo not here being present. 



The parasphenoid has much the shape that it has in T. hirundo, but the ascending processes 

 are well differentiated, and there is no median process in the interorbital region. 



The basisphenoid has a short pedicle which descends only about one half the depth of the 

 myodome, and there terminates with a free end. This free end gives attachment to the middle point 

 of the anterior edge of a stout membrane which extends backward and downward in the middle line, 

 and laterally and slightly downward on either side, and has its Insertion on the floor and sides of the 

 myodome. This membrane separates the myodome into two parts, a larger dorso-posterior portion 

 and a smaller antero-ventral one. The dorsal portion lodges the rectus externus, the ventral portion 

 lodging the rectus internus. This membrane, judging from the serial sections of the several fishes 

 that I have examined, must be found in all teleosts, in a more or less developed condition. In Scomber 

 I have already described it (Allis, '03, p. 92). 



In other respects there are, in the cranium of T. lyra no important differences from that of 

 T. hirundo. 



The hyomandibulo-palato-quadrate apparatus differs somewhat in shape from that of 

 T. hirundo, but in all important respects it closelyresembles the apparatus of that fish. Thelachrymal 

 is somewhat differently shaped, and its anterior edge is furnished with a number of stout sharp spines. 

 Two bones replace the large second infraorbital bone found in medium-sized specimens of T. hirundo, 

 thus making five bones, in all, in the series. 



According to Günther there are six bones in the series, but the specimens examined by him 

 must have been young fish, for in all of my specimens, which are large ones, there are but five bones. 

 The ridge that extends horizontally across the outer surface of the preopercular is much more pro- 

 nounced than in T. hirundo, and extends forward to that point of the third infraorbital bone from 

 which the Striae of the bone all radiate. The dorsal end of the preopercular is prolonged upward 

 and touches and is firmly bound to the outer surface of the hyomandibular, thus forming a closed 

 oval passage through which that part of the dilatator operculi that has its origin in the dilatator 

 fossa passes to reach its point of Insertion on the opercular. The spine on the opercular, at about 

 the middle of its bind edge, is much longer and stouter than in T. hirundo. 



III. Peristedion cataphractum. 

 1. SKULL. 



The orbital and postorbital portions, together, of the skull of Peristedion, occupy the posterior 

 half only of the total length of the skull, and the posterior third only of the total length of theskeleton 

 of the head. The anterior half of the skull is formed by the long, broad, flat and thin preorbital portion, 

 or snout of the fish, which is straight and inclines slightly downward. The outer surfaces of all the 

 bones are finely granulated, the granulations being arranged, in certain places, but not everywhere, 

 in faintly indicated Striae. . 



