340 G. K. GILBERT AND F. P. GULLIVER— TEPEE BUTTES. 



the same site during the long series of centuries needed for the building 

 of a core many yards in height. On the other hand, the conditions 

 could not have been essential to the existence of the Lucina, for the same 

 species is occasionally found in the shale. The local conditions actually 

 afforded by a tepee site must have included (1) a tract of firm bottom 

 several yards in extent, and (2) the dead bodies of Lucina ; but ignorance 

 of the life history of Lucina occidentalis makes it impossible to say that 

 these conditions were favorable to it. It is said that modern species of 

 the genus live in colonies and bury themselves, except the siphon, in 

 sand or mud. 



Professor Shaler suggests that the Pierre Lucina may possibly have 

 spun a byssus and thus utilized a firm support. The development of 

 the recent Lucina has not as yet been studied, so we do not know whether 

 at any stage it is attached, but a byssus has been found in the young of 

 Mya arenaria * and also in Pecten,f where the byssus stage varies in dif- 

 ferent species, and these cases of larval byssal attachment in other fam- 

 ilies, where such attachment was unknown until recently, would suggest 

 the possibility of a byssus in Lucina. 



POISON THEORY. 



Another suggested hypothesis ascribes to the tepee site some noxious 

 property by reason of which visiting mollusks were killed and thus 

 made to deposit their shells. A poisonous gas might slowly escape from 

 a buried source or poisons might arise from the decomposition of dead 

 tissues. In such case one would expect nomadic shells to be most fre- 

 quently victimized instead of the sedentary Lucina. 



CONCL USION. 



Of these various explanations the hypothesis of colonies seems to en- 

 counter least difficulty ; but our present knowledge is not sufficient to 

 establish it. 



The Buttes. 



conditions affecting distribution 



A¥ithin the tepee belt the sites of cores are marked by buttes wherever 

 the shale is exposed. Where the shale is capped by gravel deposits, even 

 if thin, the cores are not seen. This relation is readily understood. The 

 gravels represent epochs during which the controlling baselevel was ap- 

 proximately constant, when the streams meandered freely and by lateral 



* John A. Ryder: On-the Metamorphosis and Post-larval Stage of Development of the Oyster. 

 Rep. U. S. Fish Commission, 1882. 



R. T. Jackson: Phylogeny of the Pelecypoda, the Aviculidee and their allies. Memoirs Boston 

 Soc. of Nat. History, vol. iv, 1890, p. 374. 



t R. T. Jackson, op. cit., pp. 340 and 344. 



