MERRIAJr THE TH ALATToSA ri! I A 37 



This species is (|uite distantly removed from T. alcxandruc in dental char- 

 acters, and may he found to represent a distinct genus.' Although the posterior 

 mandilnilar teeth differ mucli from those of T. alezandrae the difference is only 

 one of degree. So far as known the character of the maxillary teeth seems to he 

 quite different hoth as regards form and insertion. Satisfactory comparison can 

 not he made, however, until we know more of the dentition of T. alerandrae. 



NECTOSAURUS, n. ovn, 

 Nectosaurus halius, n. p;en. ami sji. 



Platk I\", Fic. 4((-.'); Plate V, Figs. 4, (i; Pi.atk \'II, Fig. -5. 

 Type specinu'ii No. 9124 Tniv. Calif. Palac Coll. 



Fronto-parietal region simihir to that of 'f/i(il<ittii.-<(nin(s. Quadrate with 

 exterior wing. Mandible of Incertilian type. Crowns of jiosterior mandibular 

 teeth conical, acute, slightly recurved, coarsely striated. 



To this species are referred a portion of a skull constituting the type, and a 

 number of isolated bones which seem to belong here. The type was the first 

 thalattosaurian specimen to be carefully studied. Manuscript was originally 

 prepared for its description as a primitive Lacertilian but was withheld from 

 publication until more material should be obtained. 



While the mandible anil quadrate are of a lacertilian type, thalatto- 

 saurian affinities are indicated by the character of the fronto-parietal region. 

 The frontals (Fl. iv, fig. -ia) have the same form as in Thalaftosaurus. They 

 receive the premaxillaries between them anteriorly, and clasp the parietals 

 posteriorly. There is also present a portion of a prefrontal and a post-fronto- 

 orbital. A cross-section of a vertebra (PL vii, fig. 5) shows the upper arch 

 apparently firmly connected with the centrum. 



This genus contains the most primitive forms of tlie Thalattosauria and will 

 probal)]y furnish additional evidence concerning tlieir relationships when its 

 skeletal structure is better known. 



N. hal/Ks appears to he present at nearly all horizons of the Hosselkus 

 Limestone. 



In Plate v, figure (), tliere is shown a small jaw repi'esenting a type c^uite 

 common in the Hosselkus Limestone. While not seen in association with 

 certainly recognizable NccfosaHrns remains, it is doubtfully referred to that 

 genus. The dentigerous palatal element sho\vn in Plate v, figure 4 is still more 

 doubtfullv determined as belonging here. 



1 Should this type be found to be generically distinct from ThalattosauruH the generic name Scenodon will be used to 

 distinguish it. 



