Remarks on the Genus Megalichthys {Agassiz), etc. 7o 



the direction of the former across the posterior part of the 

 parietal, from the outer margin to about the middle of the 

 bone, whence the other leg then diverges outwards and 

 backwards towards the posterior margin. These grooves in 

 Osteolepis were supposed by Pander ^ to indicate the original 

 presence here of elements equivalent to the transverse 

 supra-temporal chain in Polypterus, but a careful examination 

 of the under surface of Saurodipterine cranial shields, show- 

 ing the sutures and centres of ossification, proves that this is 

 not the case, and that the grooves in question are mere 

 superficial markings. The supra- temporals are, according to 

 my interpretation, represented in this family and in allied 

 forms by the three plates, one median and two lateral, which 

 lie immediately behind the shield, and which are lettered by 

 Professor Huxley in Glyjptolcemus as supra-occipal and 

 epiotics.^ The anterior or fronto-ethmoidal part of the 

 shield in this specimen has its constituent elements com- 

 pletely anchylosed, so that not even the frontals are sepa- 

 rately recognisable. On each side the margin is slightly 

 excavated for the upper boundary of the orbit ; the anterior 

 margin is convex and expanded to form the rounded snout : 

 the nasal openings are not visible. The whole surface of the 

 buckler, besides the minute punctation of the glittering 

 enamel, is covered w^ith small scattered rounded openings, 

 apparently the orifices of " mucous " ducts. 



The posterior part of the cranial shield, detached, is well 

 shown in another specimen. This, when compared w^ith the 

 corresponding part in M. Hibherti, shows the same greater 

 proportional breadth in front seen in the last described ex- 

 ample, but the sutures betw^een its six constituent bones — 

 viz., the paired parietals, squamosals, and posterior frontals 

 — are distinctly marked; and the slime-canal apertures, 

 similarly scattered over the surface, are very much smaller. 

 The peculiar grooves on the posterior part of the shield, 

 alluded to above, are also here so slightly marked as to 

 require a lens for their definition. 



1 Op. cit, p. 11. 



2 0]). cit, j). 2, Fig. 2. On this subject see my memoir ou Tristichopterus 

 alatus (Trans. Eoy. Soc, Eclinb., vol. xxvii., 1875, p. 386). 



