VEETEBRATES. 151 



Mr. Van Home has obtained from the Warsaw beds in the neigh- 

 borhood of the mouth of Piasa creek, above Alton, two specimens 

 of the maxillary terminal form, but, unfortunately, they are in too 

 imperfect a state of preservation for the satisfactory determination 

 of their specific identity. They are quite peculiar for the exceed- 

 ingly crowded punctation, and 'one of the specimens shows quite 

 distinct widely spaced transverse undulations traversing the coronal 

 surface, recalling Deltodus cingulatus, N. and W., of the Chester 

 limestone. 



The Warsaw beds at Warsaw have also yielded a large example 

 of the mandibular median form, which is difficult to distinguish 

 from the same form associated with Deltodus occidentalis, except that 

 the principal ridge is very perceptibly more broadly rounded or 

 depressed along the crest and the alate lobe relatively stronger and 

 a little more prominent; the antero-lateral border is broken away 

 so that it is not clear how closely it resembles the typical examples 

 of the species with which it is here compared as well as its 

 resemblance to the form referred to under the head of D. trilobus, 

 from which it differs in its more robust build and less emphasized 

 coronal prominence. 



The specific identity of the teeth above alluded to, if it proves to 

 be well founded, is of enhanced interest on account of the evidence 

 they furnish on the perpetuation of the species unchanged for so 

 long a period as that involved in the deposition of probably not 

 less than 300 feet of sediments included between the earlier and 

 the latest deposits in which its remains have been found, while 

 other species subsequently appear both in the Warsaw and St 

 Louis formations. 



Geological position and localities : Warsaw limestone ; Warsaw, 

 Alton, and Jersey county, 111. : St. Louis limestone ; Alton, and 

 Monroe county, 111. 



DELTODUS PARVUS, St. J. and W. 



PI. IX, Fig. 1-5. 



Teeth of small size. Mandibular posterior form sub-trapezoidal in 

 outline, rather strongly arched and inrolled, usually a little longer 

 than wide. Antero-lateral border with a slight incurved outline, 

 basal portion slightly channeled and limited above by the narrow 

 enamel fold ; inner margin forming nearly a right angle with the 



