330 {Jan. 5, 
Cope.) 
These rays thin out to the extremity, which in some cases at least is not 
contracted. These rays are composed of appressed halves, are unsym- 
metrical with basal hook, and belong no doubt to paired fins. If those 
already described are pectoral, these are ventral, and vice versa. A series 
of them found together had much the form of either of these fins, while 
their number would identify them with the ventral. In the rays 
found together, the first only had a trenchant outer margin, while 
several had a rabbet along one side of the posterior margin. T have 
already described such a spine as pertaining to the pectoral fin of Iehthyo- 
dectes prognathus. 
The vertebra in all the species certainly assignable to this group, are 
where known, deeply two-grooved on each side, besides the pits for the 
insertion of neurapophyses and pleurapophyses, except in the cervical 
region where the lateral grooves are wanting. There are no diapophyses. 
The caudal vertebra are rather numerous but not so much so as in Amia, 
nor are they so much recurved as in that genus. 
Until the structure of the posterior cranial roof and of the scapular arch 
are fully made out, it is premature to state precisely the affinities of this 
family. So far as known they are Isospondyli with some characters of 
the Salmonidw, and some of other significance. The large foramen 
behind the prodtic bone is more Clupeoid in character. The femoral bones 
are more like those of the Plectospondyli, dividing in a measure characters 
of the Cyprinide with those of the Mormyride. The yertebre are 
Clupeoid, while the mode of implantation of teeth is peculiar. 
SyNOPsIS OF GENERA. 
I. Jaws without foramina on the inner face of the alveolar margin. 
Teeth of unequal lengths in the maxillary and dentary bones.. Portheus. 
Teeth of unequal lengths, cylindric. ...............+.0+- Ichthyodectes. 
Il. A series of foramina on inner side of alveolar wall. 
Teeth with sub-cylindric Crowns. .......6. ++ eee e eee eee Saurodon. 
Teeth with short compressed Crowns........-++-+++e0+ Saurocephatus. 
There are some other forms to be referred to this family, whose char- 
acters are not yet fully determined. Thus Hypsodon Agass., from the 
European chalk is related to the two genera first named above, but as 
left by its author in the Poissons Fossiles, includes apparently two generic 
forms. The first figured and described, has the mandibular teeth of 
equal length. In the second they are unequal, as in Portheus, to which 
genus this specimen ought, perhaps, to be referred. Both are Physos- 
tomous fishes, and not related to the Sphyranidw, where authors have 
generally placed them. Retaining the name Hypsodon for the genus with 
equal mandibular teeth, its relations to Lehthyodectes remain to be deter- 
mined by further study of the H. levesiensis. 
A species of Jehthyodectes, from the chalk of Sussex, England, is figured 
but not described, by Dixon, in the Geology of Sussex. 
A number of forms, erroneously referred by Agassiz and Dixon, to 
the genus Saurocephalus, have been referred by Leidy to a genus he calls 
