THE COMANCHE AN PERIOD. 



135 



Trigonia (Fig. 386, /) is common in both, but the species are not 

 related. It will be noticed that the pelecypods (Fig. 386, d-h) } 

 gastropods (Fig. 386, i-l), and echinoids dominate in the Mexico- 

 Texan region, the oyster family being foremost, while the cepha- 

 lopods (Fig. 387, a-c), and Aucella (Fig. 387, k, I, m), a pelecy- 

 pod, dominate the Pacific fauna, though the list of gastropods 

 (Fig. 387, d-h) and pelecypods (Fig. 387, i-q) is considerable there 

 also. Corals and crinoids are rare in both provinces. 



Fig. 386. — The Comanchean fauna of the Texan province. Echinoids: a, Holaster 

 simplex Shum.; b, Diplopodia texanum Roemer; c, Hemiaster dalli Clark. Pele- 

 cypoda: d, Anatina austinensis Vaughan; e, Homomya austinensis Vaughan; 

 /, Trigonia emoryi Conrad; g, Lima v)acoensis Roemer; h, Pecten texanus Roemer. 

 Gastropoda: i, Fusus texanus Vaughan; /, Turritella budaensis Vaughan ; k,Ceri- 

 thium(?) texanum Vaughan; I, Trochus Sp. Coral: m, Parasmilia texana Vaughan. 

 (After Vaughan.) 



The question of the cause of this distinctness has already been 

 alluded to, but cannot be positively answered. The complete dis- 

 tinctness and the contrast of aspect are obviously most completely 

 explained by a land barrier separating the two provinces, much as at 

 present, and there is now no proof that this was not the case. If, how- 

 ever, the oceans joined, the best appeal perhaps is to ocean currents 

 of different temperatures. Assuming from general meteorological 

 principles the existence of trade-winds, they would doubtless drive 

 an equatorial Atlantic current westward through the opened tract 

 and onward across the Pacific, while a northerly current might not 

 improbably descend the Pacific coast, as one now does as far as British 



