1890.] NATURAL SCIENCES OF PHILADELPHIA. 15o 



Capulus acutirostris, however, was the first species of this group of 

 gasteropods described from the Carbonic rocks of tlie Mississippi 

 basin ; and was so denominated by Hall in 185fi. The publication 

 of this diagnosis was followed in quick succession by definitions of 

 other forms by Stevens, Hall, Swallow, McChesney, Winchell, White 

 and Whitfield, and Meek and AVorthen ; so that the total number 

 of species that have been brought to notice from the carbonic rocks 

 of North America is more than two score. A part of this number 

 are, however, to be regarded as synonyms, reducing the actual num- 

 ber of species as now recognized nearly one-half. 



I. Habits of the Carbonic Calyptr^eans. 



Variation in Form. It has been noted frequently in the descrip- 

 tions of various paleozoic species of Capulus that the shells often pre- 

 sent a more or less well-defined quinquelobate appearance and 

 that the apertural margins are for the most part sinuous or crenate. 

 In the absence of salient classificatory characters these features 

 were regarded usually of much importance for specific distinction. 

 It was not until a comparatively recent date that their true 

 significance was indicated. The fact here referred to is the attach- 

 ment of fossil Capuli to foreign bodies and particularly to the 

 calyces of crinoids. The observations on this habit of the ancient 

 Capuli has been fully considered elsewhere but may be here briefly 

 summarized by stating that, in all the examples examined — upwards 

 of sevei'al hundreds — (1) the gasteropod shell invariably lies over 

 the anal opening of the crinoid ; (2) the mollusk remained in this 

 position for a considerable period, probably for the greater part of 

 life, as is shown by the shells on highly ornamented calyces and by 

 the removal of them from their places of attachment and tracing the 

 growth of the shell by the concentric grooves made on the ventral 

 plates ; (3) the growing shell followed closely the inequalities of the 

 surface upon Avhich it rested — depressions giving rise to furrows and 

 protuberances to folds or nodes ; and (4) shells simply lying on flat 

 surfaces are much more depressed and proportionally broader than 

 those clinging to the vertical or inclined portions of calyces in which 

 the anal opening is situated laterally. The third of these statements 

 is perhaps best illustrated by crinoids having low interradial areas 

 and elevated radial regions and is the probable explanation of the 

 frequent occurrence ofthe more or less distinctlyfive-lobed calyptrsean 



1 Proc. Am. Philosophical Soc, vol. xxv, 1888. 



