BY WILLIAM A. HASWELL, M.A., B.SC. 109 



The rostrum is a long spoutdike structure, the concavity in 

 which is continuous behind with the cerebral cavity. In front it 

 gradually narrows, the excavation becoming shallower, and 

 expands at the extremity into a thin sheet with a truncated 

 terminal border ; near each angle of the flattened terminal portion 

 of the rostrum is a small rounded aperture. 



The hyo-mandibular begins above in a broad extremity which 

 articulates with the surface already noticed on the auditory region 

 of the skull. Dorsally it presents a prominent ridge. The 

 hyoidean arch is incomplete dorsally and becomes articulated to 

 the dorsal mesial of the first bi'anchial arch. The latter 

 developes a short pi'ocess which, as in Hypnos, articulates 

 with the occipital region of the skull behind the surface of 

 articulation for the hyo-mandibular. The copulare of the 

 hyoid is produced anteriorly into a prominent flattened process. 

 The hyoid copula is represented by a very long, slender, ribdike 

 cartilage, which is not expanded into any broad mesial plate. The 

 basal of the first branchial arch is in very close relationship to 

 the ventral surface of the spinal column. The mesials of this and 

 the three following arches present very deep and wide muscular 

 fossa? which pass into one another across the articulation. The 

 ventral mesial cartilage of the first branchial arch developes a 

 flattened anterior process which articulates with the hyoid capula ; 

 behind it articulates with the second branchial arch at the point of 

 junction of the ventral mesial and the copulare. The second arch 

 has a strongly curved ribbondike copulare ; those of the third and 

 fourth are united ; the fifth arch has no copulare. The copularia 

 of the second, third, and fourth arches, and the ventral mesial of 

 the fifth articulate with a very wide basi-branchial plate. The 

 ventral mesial of the fifth articulates with the shoulder girdle. 



Pectoral Arch and Pectoral Fins. (Plate II., figs. 3 and 4.) 



The pectoral arch is remarkable on account of the size and form 

 of its lateral masses. The whole girdle has the form of an oval 

 hoop, with the long axis transverse, the ventral side straight and 

 the lateral portions greatly expanded. There is a narrow dorsal 



