MEXICAN FOSSIL ECHINI — JACKSON 237 



is small, situated a little posterior to the center of the test. Peristome 

 transversely oval, situated on the posterior face, just not visible in 

 dorsal view. Peristome wide, sunken, near the anterior border. 

 Plastron very narrow, highly elevated into a rostrum, near the 

 labrum in the center line. 



There are two specimens of this new species, the smaller, which is 

 more perfectly preserved, being selected as the holotype (in museum 

 of California Academy of Sciences). It measures 49 mm in length, 45 

 mm in width, and 15 mm in height. The larger specimen, which is 

 less well preserved in surface characters yet undoubtedly the same 

 species, measures 65 mm in length, 58 mm in width, and 21 mm in 

 height. L. mexicana differs from L. dumblei in having the posterior 

 interambulacrum 5 carina te. The apical disk is posterior to the 

 center instead of anterior, the primary tubercles are smaller and occur 

 on interambulacrum 5 as well as other interambulacral areas, whereas 

 they are lacking in area 5 in dumblei. In mexicana the plastron is 

 narrower and at the same time more strongly keeled than in dumblei. 



Mes6n formation, Rancho Nuevo, 2,5 km west-southwest of Meson, 

 Canton Tuxpan, Veracruz, Mexico, a few miles northeast of Tepezin- 

 titla, between Mes6n and Cerro Azul, Veracruz; W. F. Cummins, 

 collector, two specimens, California Academy of Sciences, locality 

 X62. 



U.S. eOVIRNHENT PRINTJNS OmCI: KIT 



