144 University of California Publications in Geology [Vol- 11 



also the middle cardinal. A good hinge, showing the middle and 

 anterior cardinals of the right valve, was not exposed. 



This species has been listed in a number of papers as coming from 

 the Lower Miocene, both the Turritella ocoyana and Turritella inezana 

 zones. It is rather doubtful whether it is found in these horizons. 



Gabb's type, as shown by his figure (Geol. Surv. Calif., Palaeon- 

 tology, vol. 2, pi. 5, fig. 39, 1866), appears to have a somewhat more 

 acute posterior end than the specimens here figured. Figure 6 of 

 this paper shows one of a number of specimens which came from the 

 old state survey collection at the University of California and which 

 were labeled Chionc mathcwsonii. It is not certain that this deter- 

 mination was made by Gabb. Gabb's descriptions of his localities 

 are very vague ; in this case, the locality and position are given as 

 "not rare in the Miocene south of Martinez." In this region the 

 Agasoma gravidum beds are not found directly south of Martinez but 

 to the southeast and southwest. 



ANTIGONA (ABTENA) NEGLECT A, n. sp. 

 Plate 8, figures 3, 4 and 6 

 Type specimen 11135, Coll. Invert. Palae. Univ. Calif., loe. 14. 



.Shell medium in size, heavy, subtrigonal to subovate; beaks fairly prominent, 

 well forward and strongly inturned. Anterior dorsal edge long, gently convex; 

 ventral edge regularly and rather strongly arcuate. Lunule large, elongate- 

 lanceolate, slightly impressed, being almost as long as the anterior dorsal slope ; 

 posterior dorsal margin strongly depressed into an elongate, narrow escutcheonal 

 area. Surface covered by somewhat irregular, medium coarse, lamelliform incre- 

 mental lines. Middle cardinal of left valve heavy, faintly bifid ventrally; post- 

 erior cardinal long, situated on top of lymph plate ; anterior cardinal thin, fused 

 to the side of the middle cardinal before reaching dorsal edge ; anterior lateral long 

 and prominent. A good specimen of the right valve of this species was not 

 obtained but, judging from other species of this type, we may infer that the 

 escutcheonal area on this is probably not so strongly depressed as that of the 

 left ; also, that the posterior edge is grooved to receive the corresponding edge of 

 the opposite valve. 



Dimens-wns. — Length, 59 mm. ; height, 5 mm. 



Occurrence. — University of California localities 11 and 1131. 



This form, in sculpturing and size, resembles A. mathewsonii 

 Gabb ; it occurs also in the same horizon. It differs from that species 

 in the following respects : the anterior end is less produced; the lunule 

 is larger, and the escutcheonal area is larger and more strongly de- 

 pressed. The hinge plates also differ in minor details. 



