ON THE STRUCTURE AND CLASSIFICATION 
1 PLAGIAULACIDAD.* Marsh. 
Tin, family Fobablv embraces the genera Mk.-ole.te., Gtenaeodok, Plagk^edatc, 
miodm. K.o,,lmjti,ntar, Me,.i.coi.m. and perliaps also Ihylaeoho. 
MIC'IiOLKSTES^ Plicninger, 1847. 
In describing Plagiaulax,^ Ur. Falconer fully recognized the likeness of its molars to 
those of Mk-rolestes. He gave an excellent figure of the molar of M^roJestes antiqmu^ 
obtained bv Sir Charles Lyell from the original in the Stuttgart Museum, fig. 7, 
which is much more accurate than the figure copied by Owen, Giebel and others. 
When these crowns are carefully compared with those of 31. 3Ioorei (British Museum 
Collection), fig. 7, 2 , and with the posterior molar of P. 3I%nor, (3, %a) the following 
resemblances are apparent: the inner margin of the central sub-circular valley is in 
each case raised into two tubercles ( % ) ; these are conjoined in 31. anhqmcs, and 
31. 3Ioorei, and .separated in P. minor, but in each case the antero-internal tubercle is 
Kioore 7. The molar tooth forms of the Plagiaulacidie. 1 Microlesles nnUrjuus (Stuttgart Collection'*), a 
lower molar viewed from above; la, posterior face; 16, external face, greatly enlarged. 2 c Plagiaulax 
Moorei, from above. 3 Plagiaulax minor, the lower molars viewed from above, 3 a. external face of .same 
enlargi'd Oj diameters. 4 Ptilodm Trovemartianus, lower molars viewed from above, 4 a, external face of 
same i internal tubercles, e e', external tubercles. Original. 
the most elevated of the two as well as of all the coronal tubercles ; the outer margin 
of the central valley is raised into numerous tubercles, which vary in distinctness 
but are usually five in number, the antero-external being the most prominent. In 
M. 3Ioorei we observe as an exception, a third small tubercle upon the inner margin. 
On the other hand, the differences between these molars, are seen in the deeper cre- 
nation of the outer margin of 3L antiquus, and the lateral compression of the crown, 
which brings the margins nearer together and deepens the valley into a groove more 
oiMJn at the ends than in the Plagiaulax molars. 
' Proposed by Professor Dlarsh, Am, Jour. Sc., 1881, p. 511, to embrace Plagiaulax and Ctmacodon. 
* “ Jahreahefte des Vercins fiir Vaterliindische Naturkunde in Wlirtemberg,” Band 11,1847, p. 164. taf i, 
tigs. 3 and 4. 
* liuarierly Journal of the Geological Society, August, 1857. 
* Through the kindness of Dr. E. Fraas, of Stuttgart, I have recently procured this complete set of figures of 
this type which fully confirm the drawings given by Lyell. 
