160 PROCEEDINGS OF THE ACADEMY OF [1890. 



Carbonic times the results thus far reached have been merely 

 suggestive. In other zoological groups the evidence has been much 

 more satisfactory of a reasonable co-ordination of the vertical and 

 horizontal ranges of the various species, especially in the Carbonic 

 strata of the ]\Iississippi basin. In general* the question of geo- 

 graphical distribution during geological time has appeared to elicit 

 but little attention, partly, perhaps, by reason of the many difficulties 

 encountered in such investigations ; and partly on account of in- 

 sufficient material for intelligent comparisons. It is now known 

 that many species, though perhaps originally described under sevei-al 

 different names, have a much wider geographical and geological dis- 

 tribution than has been supposed. Several of these species have 

 already been indicated ^ ; and it is certain that an extended study 

 of the forms belonging to the various zoological groups, from diverse 

 horizons and from localities widely separated geographically, would 

 be productive of many important results in the elimination of a large 

 number of now recognized species, thereby placing paleontological 

 science on a much firmer basis for more accurate deductions and 

 more suggestive conclusions relative to the true status of ancient 

 biological phenomena. The long period of comparative quietness 

 during the deposition of the Carbonic rocks of the Mississppi basin 

 and the concomitant more or less undisturbed conditions of environ- 

 ment thus imposed Avere particularly favorable to a wide geographic 

 dispersion of the various species, and to their persistency through 

 long periods of time. The majority of the species of Capulus appear 

 to be more or less widely distributed in space, especially such forms 

 as C. acutirostris, C. parvus, C. eqmlateralis and others. 



The Kinderhook forms of the genus are, on the whole, extremely 

 unsatisfactory for systematic determination, since the most of them 

 are merely internal casts. They form, however, an important 

 feature of the fauna inclosed in these rocks. The Burlington and 

 Keokuk species are very closely related, and in part extend through 

 both epochs, after which the genus is of rare occurrence in the con- 

 tinental interior. It is of considerable interest to note that this 

 numerical reduction after the close of the Keokuk was accompanied 

 by a marked depauperization of the individuals which struggled 

 through to the end of the Paleozoic. Through all the St. Louis, 

 and Kaskaskia Coal Measures the species Avithout exception are di- 

 minutive. The C. acutirostris of the St. Louis became reduced to 



1 Keyes: Proc. Acad. Nat.Sci. Phila., July 31, 1888. 



