208 PROCEEDINGS OF THE ACADEMY OF [1881. 



spires had a subtegminal mouth, and a solid test built up 

 of plates so closel}^ fitted togetlier that expansion or contraction 

 was impossible. Expansion in some parts, however, was neces- 

 sary to produce circulatory currents for the introduction of food. 

 In most Echinoderms, including all recent Crinoids, this is accom- 

 plislied by means of the pliant test and soft appendages which 

 surrounded it. The Echini alone, like the Paleozoic Crinoids, have 

 a rigid test, but the}'^ possess an external mouth, and in addition 

 to their numerous soft appendages a movable actinal membrane, 

 capable of considerable expansion, even in some cases beyond the 

 line of the actinostome. It seems to us not unlikely that the 

 h3'drospires served the purpose of gills, producing by their con- 

 tractions and dilatations the requisite circulation to introduce 

 food and expel the refuse matter. This would account for their 

 absence in the recent Crinoids and other Echinoderms, and would 

 suggest that they were probably connected with numerous soft 

 appendages along the arms, arranged perhaps in like manner as 

 the pores along the ambulacra of the Blastoids, but not as in the 

 Cystideans, in which the pores which connect with the hydrospires 

 are distributed over different parts of the body. A better knowl- 

 edge of these organs, as they exist among the three great divisions 

 of the Paleozoic Crinoids, would doubtless afford far more satis- 

 factory characters for separation than we now possess. 



In the abdominal cavity of the Paheocrinoidea, the only structure 

 which has been observed consists of a peculiar skeleton located 

 beneath the tubular canals, which from its position, in analogy to 

 other Ecliinoderms, has been referred to the digestive apparatus.^ 

 In its usual preservation, it is a large convoluted body resem- 

 bling the shell of a Bulla, open at both ends. The upper end is 

 placed beneath the centre of the vault, and the lower directed 

 toward the base. It is dilated above ; contracted below ; its 

 surface about parallel with the walls of the visceral cavity. In 

 some species it is subcylindrical, with the vertical axis the longer ; 

 in others globular or even depressed globose ; but it is always 

 truncate below, and never extends to the inner floor of the basal 

 plates. The walls are coiled without touching at any point, and 



> Meek and Wortlien, Geol. Rep. 111., v., p. 328, call it a convoluted sup- 

 port of the digestive sac. Wachsmuth, Am. Jour. Sci. Aug., 1878, p. 135, 

 terms it the " alimentary canal. ' 



