34 WATSON & Day, Notes on some Palaeozoic Fishes. 



Specimen L 10863 shows the upper surface of the 

 palato-pterygoids and of the anterior part of the para- 

 sphenoid very well, the most significant feature being the 

 presence of a distinct ridge in the middle line formed by 

 the fused pterygoids, which suggests that the whole of 

 the upper surface of the palate was not in contact with 

 the chondrocranium but only with a narrow interorbital 

 septum. From the occurrence of a " fault" in the region 

 of the quadrates which depresses the roof of the skull in 

 most specimens of the head of Dipterus we are justified 

 in concluding that there were no massive ossifications in 

 the anterior part of the brain case corresponding to those 

 in the otic region. 



Pentlandia macropterus. (Traquair.) 

 Dipterus macropterus, Traq. 



One specimen of "Dipterus" macropterus from Newark, 

 Orkney, shows fairly clearly the structure of the top of 

 the head, the bones being represented by an impression, 

 squeezes from which are readily intelligible. The bones 

 of the left side are in place, whilst those of the right are 

 mostly displaced or missing. The figure given by Traquair 

 agrees so far as it goes with our specimen, which however 

 shows many additional elements. The significant features 

 are, that the bones are loosely articulated, that there is no 

 solid covering to the anterior end of the head, and that 

 there are no median elements in advance of that which 

 lies at the extreme back of the skull. This difference is one 

 of importance. We shall show in a later part of this paper 

 that it depends on the fact that "Dipterus" macropterus 

 is a definite stage in the evolution of Dipnoi, derived from 

 Dipterus and leading towards Scaumenacia ; we therefore 

 give it the new name of Pentlandia, after the strait which 

 separates its two localities, John o' Groats and Deerness. 



