8 PROCEEDINGS OF THE NATIONAL, MUSEUM. vol. 31. 



Gonzalez, in the State of Tamaulipas, Mexico. Discovered by Mr. 

 R. A. Bishop and collected by Messrs. Bishop and John M. Miiir. 



Type.—Dona.ted to the United States National Museum by the 

 firm of Smith, Newell, and Bishop, owners of Las Flores hacienda. 

 Cat. No. 32499, U.S.N.M. 



Geologic position. — Upper part of Mendez shale, which is an Up- 

 per Cretaceous formation corresponding in age approximately to 

 the Taylor marl of Texas. 



TAMPSIA CHOCOYENSIS, new species. 



Plates 5-8. 



Discovery a/nd occurrence. — This species is based upon a colony 

 of rudistids found in April, 1921, by A. W. Beckley and the writer 

 in reddish shale in the upper part of the Mendez formation. The 

 colony had been eroded from its position in the shale and was badly 

 shattered. All the fragments that could be found were collected, 

 and when as many of these as possible were fitted together they were 

 found to include two attached lower valves, well preserved though 

 incomplete at their lower extremities, and a dozen or more less com- 

 plete lower valves and fragments. The two attached individuals 

 (pi. 5) are here designated the type. A portion of the shell of one 

 individual (pi. 8), perhaps belonging to this same colony, was found 

 at this locality in 1919 by A. E. Fath and Eugene Stebinger. 



Description. — In general form and in all the characters that may 

 be regarded as generic this species is identical with that of Tampsia 

 hishopi. The principal features which distinguish it from that 

 species are (1) the coarser and rougher character of the growth 

 lamellae, which tend to form irregular imbricating layers; (2) 

 the sharper and somewhat stronger longitudinal undulations or ribs, 

 which, however, are very irregular in their development; (3) the 

 greater breadth of the anterior siphonal channel (E), the sides of 

 which are also rougher and sometimes marked by faint longitudinal 

 folds; and (4) the pronounced irregularity in the development of 

 the posterior siphonal channel (S), which in some individuals is 

 very shallow and in others is broken into a main and a subordinate 

 channel by an intermediate rib. In one of the individuals of the 

 type pair the bottom of the broad posterior siphonal channel is cut 

 by a narrow, deep subordinate channel (pi. 6), in front of which is 

 another narrow but shallow subordinate channel. 



The largest of the two attached shells of the type pair exhibits 

 the following maximum dimensions: Length, 200 mm.; diameter 

 at top, 130 mm. ; diameter at the incomplete bottom, 90 mm. ; diam- 

 eter of inner cavity, 63 mm. at top and 43 mm. at bottom. 



Locality. — Found in red shale in a gully known as El Colorado, 

 on Chocoy hacienda or ranch, 1^ kilometers northwest of Omaha 



