Vol. 4] Weaver. — Palaeontology of the Martinez Group. 



117 



extend to the shell margin. The base and the anterior end are 

 closed and the posterior end gapes considerably. The lip extends 

 slightly outward in the upper half and then is obliquely trun- 

 cated inward toward the base. 



Dimensions: — The length of the specimen described is 69 mm. 

 The maximum thickness is 37 mm., and the distance from beak 

 to base 46 mm. 



Occurrence: — This species is found at numerous localities 

 south of Martinez; also on the arsenal grounds at Benieia. It 

 is characteristic of both upper and lower beds. 



Thracia karquinesensis, n. sp. 



Pl. 12, Fig. 5. 



The shell is thin, moderately convex and marked with con- 

 centric stria?. The beaks are prominent and located about one- 

 third the distance from the anterior end. The base is nearly 

 straight. The upper margin of the wing is nearly parallel to the 

 base. The anterior end is rounded and the posterior somewhat 

 produced, the body of it where it joins on to the wing sloping 

 downward toward the base and making an angle of about forty- 

 five degrees. 



Dimensions : — The maximum length of this specimen is 29 

 mm., and the distance from beak to base 15 mm. Only one speci- 

 men has been found. 



Occurrence : — This form was found about two and one-half 

 miles south of Martinez, on the west side of the road to Walnut 

 Creek. It occurred in the upper beds of the Martinez. 



GASTEROPODA. 



Architectonica tuberculata, n. sp. 



Pl. 12, Figs. 7 & 7a. 



The shell is small, the spire low, and the number of slightly 

 convex whorls present is six. The surface is mai'ked by a number 

 of small tubercular ribs. There are eight ribs to each whorl. 

 This description is taken from a cast. 



Dimensions: — The diameter was found to be 9 mm., and the 

 distance from base to apex 2 mm. 



