Sir Philip Grey-Egerton — On so me New Pycnodonts. 51 
small teeth are intercalated between the rows, in others the larger 
teeth are repl^ced by two smaller ones, as in the specimen described 
in this article ; but. in every case these teeth are smaller than those 
of the principal row. In the genus Gtjrodus the dental formula 
does not appear to be subject to these irregularities, there being con- 
stantly four rows in each mandible, and five in the vomer. In this 
genus the outer row comes next in size to the principal row, and all 
the teeth have a central eminence surrounded by a fossa. In Microdon 
also the teeth of the outer row of the four are next in size to the 
principal ones. 
Palceobalistum of de Blainville has three rows, the component 
teeth being arranged obliquely. In Mesodon of Wagner the teeth 
are oval, concave, and notched on the periphery. Heckei 1 has added 
two genera to the family, — Stemmatodus having three rows of teeth 
on either side with notched borders and granulate crowns ; and 
Coelodus described as having three rows on each mandible, elliptical, 
with a slight depression on the surface of each tooth. He has, 
moreover, upon the evidence of anatomical structure combined with 
the dental characters, remodelled the arrangement of the species of 
this family. 
Microdon hexagonus and rugulosus of Agassiz are referred to 
Gyrodus, as is also Microdon truncatus of Wagner. Pycnodus Itieri, 
Sauvanasii, Bernardi, Egertoni, and Wagneri of Thiolliere ; Pycnodus 
umbonatus and Hügii of Agassiz ; and Pycnodus formosus and Reussii 
of Wagner, are removed to the genus Microdon. Gyrodus macropterus 
of Agassiz, and Pycnodus liassicus mihi, are joined to Mesodon. 
Pycnodus rhombus of Agassiz goes to Stemmatodus, and Pycnodus 
orbiculatus of Agassiz to its pristine genus Palceobalistum of de Blain- 
ville. The new genus Coelodus, in addition to the many fine species 
of entire fish found in Austria, is made to include Pycnodus rhombus, 
and Glossodus anguslatus of Costa and Pycnodus Mantelli of Agassiz. 
On comparing the Folkestone fossil with these several forms, 
there is no doubt but that it mostly resembles the genus Coelodus of 
Heckei. A detached tooth from the outer row might indeed be 
mistaken for a Gyrodus tooth if the crown were at all ground down, 
but in a young tooth with the surface intact the difference is very 
discemible. In specimens having the ranks of teeth preserved 
there can be no mistake, as in Gyrodus the teeth of the outer row 
are next in size to the principal teeth, whereas in Coelodus they 
diminish progressively from the inner to the outer series. The 
number of the dental ranks in the hinder part of the jaw agrees 
with Heckel’s formula, and, as I have stated before, I do not con- 
sider the irregularity of the subsidiary ranks in the anterior portion 
as indicative of generic Variation. Assuming then that this mandible 
belongs to Coelodus, it is manifest that it cannot be identified with 
any of the species of the genus yet described. It is of larger size 
than the Coelodus Saturnus figured by Heckei, and differs from that and 
all the other species in having the teeth of the second row more 
numerous and more elliptical. I propose to call it Coelodus ellipticus. 
1 Beiträge zur Kenntniss der fossilen Fische Oesterreichs, pt. 2. 
