l8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



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 of tlie loop, X 4. paratype U.S.N.M. No. 124202!. 19, A 

 slightly larger specimen than the preceding in dalliniform 

 stage showing descending branches and remnantal septal at- 

 tachments, X 4, paratype U.S.N.M. No. i24i9oh. 20, Frag- 

 ment of brachial valve showing hinge plate, sockets, and 

 socket ridges, X 4, paratype U.S.N.M. No. 124190J. 21, In- 

 terior of another brachial valve, X 4, showing adductor scars 

 indistinctly, paratype U.S.N.M. No. I24i90e. 22, Cardinalia 

 of an adult brachial valve, X 4, showing crural processes 

 and hinge plate with upturned edge, paratype U.S.N.M. No. 

 1241901. 23, 24, Two views, X 4. of the interior of an adult 

 brachial valve, one (23) tilted and the other not, showing 

 hinge plate socket ridges, almost obsolete median septum, and 

 also the dental plates of the pedicle valve, paratype U.S.N.M. 

 No. i24i9of. Horizon and locality same as above. 



C. Psilothyris tamarinda ( Sowerby ) 14 



25, Interior of the brachial valve showing cardinalia and nearly 

 obsolete median septum, X 3, figured specimen U.S.N.M. No. 

 128222. Cretaceous (Aptian — Lower Green Sand), Faring- 

 don, Berkshire, England. 



Plate 4 



A. Psilothyris occidcntalis Cooper, new species n 



I, 2, Side and interior tilted views of a specimen in pre-campagi- 

 form stage 4.5 mm. long showing the pillar before growth of 

 median septum, and descending lamellae, about X 14 and X 10, 

 respectively, paratype U.S.N.M. No. I24202g. Mural lime- 

 stone, a small hill 300 yards east of U. S. Highway 80, NWi- 

 SWiNEi sec. 36, T. 2^ S., R. 25 E., Bisbee Quadrangle, 

 Cochise County, Arizona. 



B. Gonmarcula arizoncnsis Cooper, new species 7 



3, 4, Interior and side views of a brachial valve 3.6 mm. wide 

 showing remnants of pre-campagiform hood, pillar, and begin- 

 ning of loop ring, about X i/, paratype U.S.N.M. No. 124199. 

 5, 6, Side and interior views of brachial valve showing the 

 adult loop, about X 4-5, paratype U.S.N.M. No. 124220. Hori- 

 zon and locality same as in text; (3) and (4) from Arizona. 

 (5) and (6) from Sonora, Mexico. 



Abhrcz>iations 



ab = ascending branch of loop g = groove of pillar 



cb = crural base p = septal pillar 



cp = cardinal process pf = remnant of pre-campagiform flange 



dl = descending branch of loop s = septum 



e = ear of loop sdl = scar of broken descending lamella 



(Drawings by Lawrence B. Isham.) 



