272 SCT.-EXID-F, 



slightly concave and porous, and terminates in an exceedingly nar- 

 row, styliform posterior part. The mucifcrous channel of the man- 

 dihula is divided by voiy d(>licate transverse bones into three largo 

 cavities and several small ones near the symphysis. The hypotym- 

 panic is joined to the prcetympanic by a narrow strip of cartila- 

 ginous tissue, the other tympanic bones being joined together by 

 more or less distinct sutures. The mesotympanio is very small 

 and narrow, without foramen. There is a small cav-itj', closed bj' a 

 membrane only, between the ^jroe- and epitympanic, and the latter 

 exhibits immediately behind that cavity a slightly curved ridge, sur- 

 rounding one-half of a rather wide foramen, Tlie jiterygoid is tri- 

 angular, and extends to the mandibulary joint ; it touches the ento- 

 pterygoid by one of its angles, without forming a ILnear suture with 

 it. The entopterygoid is formed by a moderately strong osseous 

 strip along the suture with the palatine bone, all the rest being thin 

 and fragile, Uke the adjacent part of the pra^tympanic. Tho pala- 

 tine bone has ar triangular shape, and has one of its sides free. 



The upper sm-face of the skull is entirely occupied by deep and 

 wide cavities, separated from one another by more or less thin bony 

 bars. The occipital crest is formed as in Sctoina amazonka, but 

 there are no cavities in the supraoccipital ; the cavities, too, have a 

 more or less different form. The occipital crest bifurcates, and emits 

 two bars, to form the central and largest ca^'ity : this cavity is 

 elongate, quadrangular, with two pairs of sides, with a posterior 

 acute angle and a very obtuse one in front, and ^dth the lateral 

 ones slightly exceeding a right angle : the posterior pair of the sides 

 is at least three times as long as the anterior. There are five other 

 cavities besides, on each lateral half of the upper surface of the skull 

 (several small ones not included which are situated on, or near, the 

 suprascapula) : — 



1. A pentagonal cavity between the central cavity and the upper 

 margin of the orbit. 



2. A pentagonal ca\'ity between the former and the posterior in- 

 fraorbital bone : there is another small one attached to it, interme- 

 diate between the prasopercular channel and the frontal cavities. 



3. An oblong, (juadi'angular ca\dty between the central ca%nty and 

 the turbinal bone. 



4. An irregularly half-cylindrical cavity, formed by the turbinal 

 bone. 



5. An incomplete cavity, situated at the side of the occipital crest, 

 and behind the cavity described under no. 1. 



The infraorbital arch is composed of six broad, thin bones, with 

 a stronger orbital ridge, from which radiate other transverse bars, 

 di\'iding the infraorbital channel into as many cavities. This chan- 

 nel has the same relation to other parts of the muciferous system as 

 in Scimia amazonica. The first and second infraorbitals apparently 

 form one single bone with five or six cavities ; the third has two 

 transverse bars, the posterioi' ones severally one. The structure of the 

 pneopcrcidar channel is the same as in the other species mentioned, 

 but two of the bars are j-alher strong, and terminate in two promi- 



