36 



posite along the lips. One feature not yet indi- 

 cated allies this type to the first mentioned tribe 

 — the presence of the pair of slender bones sus- 

 pended beneath the interbranchial series for the 

 attachment of the muscles which separate the in- 

 ferior pharyngeals; these bones appear to be 

 wanting in all the Oatostomi. 



A new generic division therefore seems needed, 

 for which the characters specified suggest the 

 name. 



Mylopharodon, Ayres. 



Scales, Jins, and lateral line very similar to 

 those of Lavinia. Mouth rather large. Lips 

 not corrugated. A thickened deposite, slightly 

 rugose along the inner surfuce of each lip. Pha- 

 ryngeal teeth in two rows ; those of the outer row 

 blunt, truncate abruptly. 



The position which this genus must occupy 

 has been already shown. 



It may here be stated that for the fish with 

 which this is associated in name by the fishermen, 

 the one already described by me as Gila grandis. 

 a new genus must presently be constructed. 



M. robustus attains a weight of six to eight 

 pounds, being thus the second in size of the Cal- 

 ifornia Cyprinidae with which we are yet acquain- 

 ted. 



The following communication was received 

 from Dr. Antisell : 



I take the liberty of submitting to the Acade- 

 my of Natural Sciences of San Francisco, the 

 accompanying fossils derived from San Luis Obis- 

 po County: they are found occupying a very ex- 

 tensive tract of country, not being confined to 

 the above named county, but well marked there 

 and having made a more close investigation of 

 the extent of their distribution in the Valley of 

 Santa Margarita, I am better enabled to local- 

 ize them and I present a rough diagram, giving 

 a section of that Valley. The trail through 

 from the Salinas Valley to the town of San Luis 

 Obispo passes along this valley whose western 

 limit is the range of the Coast Mountains, and 

 its eastern, the Salinas river from which it is sep- 

 arated by a low granite range — when this section 

 is made, the distance between these two points is 

 about nine miles. The Valley lies to the East- 

 ward and is about 1000 feet above sea level: the 

 strata are very much contorted and bent by au- 

 gitic and magnesian (Talcose) rocks which are 

 protruded in a few places and since which the 

 whole surface has been smoothed down and denu- 

 ded by current-actions. The rocks on the west 

 side of the Valley are sandstones, grits and con 

 glomerates having a general dip to N. West, 

 varying from 20° to 50°, intersected by Fels- 

 pathic, Amygdaloid, and Augitic trap which are 



the elevating agents of the littoral range of hills 

 On the East of the Valley as stated is a granitic 

 axis upon which the sandstone conglomerate resta 

 conformably, although the beds have, by no 

 means the same thickness as upon the west side; 

 upon those beds of sandstone just mentioned re- 

 pose the fossiliferous layex's, from which they 

 are separated by a few feet of aluminous rocks, 

 with lamellar, flinty layers, pi'esenting in some 

 parts a distinct onyx-lamina: this layer as it is a 

 constant one, is that which indicates alike the 

 position of the fossiliferous bed, and the intruding 

 effects of the trap rocks ; the /ossil beds always 

 rest upon this layer, and in some places are not 

 more than four feet apart from it. It is the 

 western limit which this bed forms, for I have 

 not found it appear in the eastern side. 



The fossiliferous beds dip generally eastward 

 or south-east, and have no defined synclinal axis, 

 but repose conformably on the subjoined flinty 

 bed. These beds in a few cases occupy the low- 

 er portion of the Valley, but at its southern ex- 

 tremity, it is elevated and forms the low, rounded 

 whitish hills which are so prominent a feature in 

 the landscape. They occupy a width in the Val- 

 ley from % to nearly 3 miles and having a direc- 

 tion of N. 10° W. (Magnetic.) The total thick- 

 ness of these beds, I do not think exceeds 450 

 feet and may be conveniently divided into four 

 beds, beginning at the bottom of the Series. 



1. Bed. Reposing on the flinty layers — about 

 200 feet thick a fine whitish sandstone with lay- 

 ers of Ostrea interstratified; these shells are general 

 ly in layers from 2 to 4 feet thick and connected 

 together by a calcareous paste including fine grains 

 of rounded quartz pebble. The sample of oyster 

 which I forward is a fair specimen of the size 

 and form, though not by any means the largest ; 

 the largest I have seen measured 14 inches long, 

 by seven inches wide, the great weight of these 

 shells is an objection to their transport; the thick- 

 ness the under shell attains is remarkable, 6 inches 

 in some cases. I send a portion of an upper shell 

 to show a characteristic which exists in many 

 though not all the specimens, viz: the thickness 

 of the proeess near the hinge. I have not a 

 work by me to name this shell, and I am not fa- 

 miliar with it as fossil. I think I have two oth- 

 er species well marked. 



The 2nd bed lies above the first from which it 

 is separated by quartz grit — it contains a mass 

 of broken shells forming a calcareous mass and 

 layers of oyster and Pecten— the Pectens are 

 large, rarely perfect, and when so, in such a soft 

 condition that it is difficult to preserve them. — 

 Some specimens resemble closely the Pecten Ja- 

 cobajus ; this varies from 70 to 85 feet in thick- 

 ness. 



The 3d bed varies from 60 to 90 feet thick, is 

 made up almost completely of the white calcare- 

 ous cement and quartz pebble ; the fossils in it 



