CALAM0CRIN1 S DIOM] D I 



those of iimin of the Camerata; and the passage of the Interradials to 

 small ventral plates in several palaeozoic genera corresponds to the structure 

 of the perisome in ( lolamoci iuus. 



The interradial plates of Taxocrinus intermedins (Geol. Survey of Illinois. 

 VIII. 199) can. according to Wachsmuth and Springer, be traced in both 

 the specimens they describe to the ventral side, the plates of the third 

 row forming a sharply defined edge, against which the plates of the ven- 

 tral covering rest. 



The junction of the perforate and imperforate perisomatic plates is shown 

 in Plate IX. Fig. 2, which represents some of the smaller perforated plates 

 close to the side plates adjoining the loud groove near the central part 

 of the disk. As is seen in Plate IX. Fig. 2, the number of pores to each 

 plate varies greatly; sometimes the pores are merely openings in the 

 coarser reticulation (Plate IX. Fig. 4, p), or there seems to be a discon- 

 tinuity in the limestone meshwork, leaving large irregularly lobed open- 

 ings, as in Plate IX. Fig. 3. //. In the plates close to the food groove 

 the reticulation becomes somewhat indistinct, and more or less lamellar in 

 structure, giving the surface of the perforated plates a spongy appearance, 

 as in Plate IX. Fig. 5, p. A transverse section across one of the perforated 

 plates shows that the canals into which these pores of the surface of the 

 plates open are more or less curved, and form broad irregular canals in 

 the meshwork of the plate, passing either completely through or terminating 

 in a cul-de-sac (Plate IX. Fig. 6,j»). The reticulation of the perforated plates 

 is also somewhat coarser than that of the imperforated plates, especially 

 those of the lower rows near their junction with the radials. 



The plates pierced for pores pass in Calamocrinus very gradually info 

 the so called interradials : this plating is very highly developed in Extra- 

 crinus and in Apiocrinus (de Loriol); and they apparently (Von Koenen) 

 do not differ in any way from the ventral disk of the Ichthyocrinid.e. with 

 which Wachsmuth. however, said originally that " they cannot in the re- 

 motest degree be homologized " ; * but he and Springer have since come 

 to a different conclusion. 



The water pores are very numerous in some species of Pentacrinus. 

 They are well figured by Midler for P. asterius. and by Carpenter for 

 P. Wyville-Thomsoni, who mentions them in P. Milleri and P. decorus. 

 The angles forming the junction of the food grooves round the mouth 



Am .Tour. Sci., Vol. XIV. p. 190. 



