^THALION 



127 



but exhibits most of the characters of the species in the counterpart halves of a 

 slab of clay. The mandibular suspensorium is clearly inclined forwards, so that 

 the articulation of the lower jaw must have been directly beneath the hinder part 

 of the orbit. The hyomandibular bone (Inn.) bears a rather long process for the 

 suspension of the operculum (op.), which is too imperfect to show its shape 

 completely. The angle of the preoperculum (pop.) is much expanded, and its 

 tapering ascending limb is upright. The suboperculum (sop.) must have been 

 about four times as broad as deep. Fifteen branchiostegal rays (br.) can be 

 counted, the upper seven being expanded and in close series, the lower eight being 





':--:''-.■'. ' 



op cp. pop. 



Fig. 39. — JEthalion vahlensis, A. S. Woodward; type specimen, nearly one-half nat. size. — Weald Clay; 

 Southwater, Sussex. British Museum, no. P. 10-140. In-., branchiostegal rays; cl., clavicle; hm., 

 hyomandibular; op., operculum; pop., preoperculum; ptt., post-temporal; scl., snpraclavicle ; sop., 

 suboperculum. 



narrower bars and more widely spaced. All the opercular apparatus is smooth, 

 not ornamented. The total number of vertebras is about GO, half being in the 

 abdominal region. The centra are about as long as deep in the anterior part of 

 the caudal region, but are somewhat shorter than deep both in the abdominal 

 and in the hinder part of the caudal region. They are well ossified, and their 

 primitive double cone is strengthened by secondary bone arranged in fine, close, 

 longitudinal ridges. The ribs are stout, apparently borne on very short transverse 

 processes, and extending to the ventral border of the fish. The fixed neural and 

 hasmal arches in the caudal region are also stout and gently arched. The hinder 

 end of the vertebral column turns only slightly upwards, and its haemal arches are 

 expanded without fusion. The intermuscular bones are much obscured by the 

 scales in the fossil, but there are traces of them above the vertebral column 

 in the abdominal region, and both above and below this column in the caudal 

 region. 



The post-temporal bone (ptt.) is a thick plate, almost triangular in shape, and 

 the supraclavicle (scl.) is a deep and narrow bone. The clavicle (cl.), as shown in 

 impression, is expanded into a large smooth plate above the pectoral fin, which 



