CRINOID GENUS SCYPHOCRINUS 41 



to definitely settle their relations. The descriptions of the openings given by 

 Wachsmuth and Springer, already mentioned, are quite complete for the genera 

 in which they had then been observed. The important points to remember 

 are: that these openings are situated at the margin of the tegmen, in the 

 brachial zone, where the dorsal and ventral walls meet; that they do not 

 penetrate the plates, but lie at their angles or within the sutures ; and that they 

 stand in close relation to the arm-openings. Thus they have not the structure 

 of madrepores. Taking Batocrinus as a normal example, it will be seen that 

 the pores are small, enter the calyx wall obliquely at the side of the arm- 

 openings by passages which connect directly with the food canals; in other 

 words, the passages leading to the pores are branches of the food canals (see 

 Rev. Pal., vol. 2, pi. 19, fig. 4; and N. A. Crin. Cam., pi. 27, fig. 3a). To 

 better show the exact relation of the grooves leading from these openings to 

 the food canals I give an enlarged transverse view of the calyx wall in 

 Batocrinus at the level of the arm-openings (text-fig. 17); thus they branch 

 from the food groove leading to the arms exactly as pinnule grooves would. 



In Dolatocrinus the openings take the form of narrow slits, running ven- 

 tralwards from the dorsoventral margin where the main point of exit was 

 located (N. A. Crin. Cam., pi. 25, figs. 6b, c, d; pi. 26, figs. \a, $b, 6a) : here 

 the number of openings is greatly increased, amounting to six or eight in 

 D. grandis M. and G. (Bull. 4, 111. St. Mus. Nat. Hist., pi. 2, figs. 2, 3). The 

 appearance of the pores in Eucladocrinus and Cactocrinus respectively is shown 

 in N. A. Crin. Cam., pi. 84, fig. 5 ; P 1 - 57> %• IO >" P 1 - 5$, fig. 6. 



Coming now to the new material, a very instructive case is found in the 

 genus Cyphocrinus S. A. Miller (Hyptiocrinus W. and Sp.), one of the few 

 crinoids in which the biserial arm structure extends down into the calyx wall — 

 a fact which is seen only in very well-preserved specimens (text-fig. 18). The 

 cuneiform secundibrachs give rise to a series of plates from each longer face 

 which lead to elongate pores in the brachial zone, two pinnule ossicles being 

 incorporated in the dorsal wall; and further incorporation of pinnules upon 

 the tertibrachs occurs, producing as many as six pores to the interradius. The 

 course of these series is similar to that of the fixed pinnules in Glyptocrinus 

 as they would be in the early stages. 



The decisive evidence, however, is found in the Silurian genus Marsipo- 

 crinus. On account of the silicified condition in which the specimens are 

 usually found in the American localities, the presence of the interbrachial 

 pores has not hitherto been noted ; but some extremely fine specimens obtained 

 in recent years from Tennessee not only show their existence in this genus, but 

 demonstrate beyond the slightest doubt that these openings are in the sockets 

 of pinnules originating below the bases of the free arms. The openings them- 

 selves are small, usually obscure, and there is nothing on the dorsal side to 



