86 
ox the occurrence of strepsodus sulcidens, handcock and 
attiiey, in the yorkshire coal measures. 
by edgar d. wellburn, f.g.s. 
Introduction. 
Whilst looking tlirough some fish-remains in the Museum, 
Bi'ighouse, Yorkshire, I found a fine mandibular ramus which 
was labelled Meyalichthys, but which on examination proved to 
belong to the fish Stre2:)sodus sulcideris. As it is the first time 
this fish has been found in the Yorkshire Coal Measures, and as 
the specimen shows some points of great interest, I judged it 
worthy of a brief description. 
Description of the Specimen. 
The specimen is that of a mandibular ramus — -imperfect 
posteriorly— with three fine laniary teeth, seen from the inner 
side. In order to understand aright the points shown in the 
specimen as figured on Plate XVIII., the author considers it 
advisable to give a brief description of the structure of the 
mandible of the Rhizodontid?e. In that family the mandible is 
of a very complex structure, and as shown by Dr. Traquair, 
r.R.S., is built up in the following manner, viz. : — There is first 
a dentary bone which is deep and thick at the symphysis, from 
which point it tapers backwards, and bears a series of small 
teeth, with one large laniary tootli in front. Below this bone 
there is a series of three or four plate-like lenticular bones, the 
hindermost of which corresponds to tlie angular bone, whilst the 
others are termed the infradentaries. A thin, splenial lamina 
forms tlie inner wall, and between these and the dentary are 
a series of three or four stout lenticular bones, the laniaries, 
each of which bears a strong laniary tooth. 
On again turning to the specimen, it is at once apparent 
that the inner wall of the jaw, or splenial, is absent, but the 
outer and inner segments are present. 
Of the outer wall, or segment, the inner side of the first 
and part of the second infradentaries are shov/n, the dividing 
