— 49 — 



straight; beaks moderate, meeting in a medial line; anterior outline 

 slightly incurved above, but rounded on lower half; base moderately 

 curved, rounded posteriorly. Length of largest, 2.50 inches; height, 2; 

 diameter of shell, about 1.20. Truncation quite variable. As the 

 many specimens obtained did not agree with any described by Gabb, 

 and were accompanied by many of his C. inermis and C. viathewsoni, 

 I suspected them to be the C. xquilateralis Meek, described from the 

 Cretaceous of Vancouver I., B. C. On sending one to Dr. White, in 

 Washington, to compare, he decided it was different, and could give no 

 name for it. Cretaceous of Santa Ana Mountains, Orange County, 

 Dr. S. Bowers. The collections made in that most southern locality 

 in which Ammonites have been found in California (except the old San 

 Diego coal mine), were enumerated in the Report of the State Miner- 

 alogist for 1890. There were several other species which may prove 

 new, but in too imperfect a condition to describe. The ^' Exogyra 

 costata Say" of the list proves not to be that, but the species is 

 uncertain. 



Corbula triangulata n. sp. (PI. IV, Fig. 42.) 



Shell doubly trigonal, higher than long, with four nearly equal 

 triangular surfaces. Valves equal, the disks being nearly right-angled 

 triangles, higher than wide; the beaks prominent, acute; anterior 

 margin slightly incurved; posterior straight, more acutely ridged later- 

 ally; surface crossed by about thirty undulations, parallel to lines of 

 growth. Basal margin moderately curved. Anterior face of shell 

 triangular-cordate, slightly concave, with edges of valves projecting 

 vertically in upper half. Posterior face similar, but twice as large; 

 concave above, and edges of valves less prominent; central area convex, 

 and umbonal ridges forming a sharp raised margin on each side. 

 Hinge unknown. Length of base, 0.30; anterior height, 0.30; posterior, 

 0.40; breadth, 0.30; at umbos, 0.20. 



This curious shell was found by Mr. Fairbanks only at base of Pt. 

 Loma, in Cret. A, and only the entire shell described occurred, with one 

 other broken valve. I was therefore doubtful whether to call it a 

 Corhula or Nucula, or something else, but finding that Conrad has 

 described somewhat similar Tertiary species, as Corhula curta and 

 C. elevata, from Maryland, I venture to propose the above name. 

 When the hinge can be examined, a subgeneric name will probably be 

 found advisable. 



Mytilus dichotomus n. sp. (PL V, Fig. 64.) 



Very similar to ^'' Sepiifer dichotomus^' Gabb, but without any trace 

 of a septum inside the beaks. Outside also sculptured, as in Modiola 

 ornata Gabb, and in several Tertiary or living species of this family. 

 (Unfortunately the umbonal end of the specimen figured was broken 



