120 jD?*. R. S. Traquair—On the Genus Mrgalichthys, 



be seen to differ in shape from that in the ordinary species, in being 

 proportionally broader in front. The plates of which it is composed 

 seem pretty completely fused together, as the indications of their 

 original separation are slight and principally seen posteriorly. Near 

 the hinder margin are also seen certain grooves like those observable 

 in a similar situation on the cranial shield of Osteolepis and Diplopterus. 

 One of these passes transversely across the middle of the squamosal 

 element : another is V-shaped, one leg of the V continuing 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 supratemporal chain in Poiypterus, but a careful examina- 

 tion of the under surface of Saurodipterine cranial shields, showing 

 the sutures and centres of ossification, proves that this is not the 

 case, and that the grooves in question are mere superficial markings. 

 The supratemporals 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 Prof. Huxley in Glyptotcemus as supraoccipital and 

 epiotics." The anterior or fronto-ethmoidal part of the shield in 

 this specimen has its constituent elements completely anchylosed, so 

 that not even the frontals are separately recognizable. On each side 

 the margin is slightly excavated for the upper boundary of the orbit ; 

 the anteiior 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 with 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 with the corresponding 

 part in M. Hihberti, shows the same greater proportional breadth in 

 front seen in the last described example, but the sutures between its 

 six constituent bones, viz. the paired parietals, squamosals and pos- 

 terior frontals, are distinctly marked, and the slime-canal apertures, 

 similarly' scattered over the surface, are very much smaller. The pecu- 

 liar 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. 



Keturning to the former head (Fig. 3) we find that though the 

 operculars are gone, and most of the other superficial bones fractured 

 and badly seen, the maxilla and mandible occupy their positions. 

 The maxilla (m x), the anterior portion of which is deficient in this 

 specin)en, at once attracts attention by its narrow shape. It is 

 shown in its entirety in the specimen represented in Fig. 4, where it 

 is seen to differ from that of M. Hihberti in the much smaller depth 

 of its posterior expanded portion, that being contained 4^ times in 

 its length, whereas in that species it is only contained about 3 times, 



1 op. eit. p. 11. 2 op^ gi(^ p. 2, fig. 2. On this subject see my 



memoir on Tristichopterus alatus, Trans. Roy. Soc. Edinb. vol. xxvii. (1875) p. 386. 



