36 CATALOGUE OF THE BLASTOIDEA. 



but on the other hand, we have little doubt that Hall 1 was right in describing the 

 posterior deltoid as divided into two parts by an intercalated anal plate which had 

 escaped Roemer's notice. Hall stated that he had never been able to find evidence 

 of a distinct suture-line bounding the supposed lanceolate portion in the middle of 

 either of the four normal interradii, " while on the anal side, the narrow plate which 

 is nearly of the same form, is limited by a distinct suture-line." 



Both Montgomery 2 and Barris 3 , who have lately described new species of Elcea- 

 crinus, have adopted Roemer's analysis of the calyx as modified by Hall ; and we 

 think that there can now be no doubt that while the four anterior interradii of this 

 genus are perfectly normal in their characters, the posterior deltoid is divided into 

 two parts by an intercalated anal plate, as is well shown in PI. XVIII. fig. 19. 



The deltoids of the type which was described by Troost as Pentremites Reinwardti, 

 and, in accordance with Shumard's suggestion, has since been generally known as 

 Troostocrinus Reinwardti, appear to present a very striking peculiarity, of which we 

 only became fully aware after the completion of our Plates and during the passage 

 of this sheet through the press. In Roemer's first account 4 of the species, he 

 described and figured the deltoids as appearing on the exterior of the calyx, and of 

 about the same relative size as those of Pentremites pyriformis (PI. II. figs. 24-30). 

 But at the same time he stated that the interradial suture often appeared to reach 

 the apex of the triangular area between every two ambulacra ; and in a later account 5 

 he expressed his conviction that he had mistaken cracks in the calcite for the radio- 

 deltoid sutures, and " dass in der That die seitlichen Nahte der Gabelstiicke stetsbis 

 zur Spitze des Scheitels verlaufen und Deltoid-Stiicke von der friiher angenommenen 

 Grosse und Lage also nicht vorhanden sind " (PI. XII. fig. 11). 



Hambach 6 , however, subsequently figured an individual in which a relatively large 

 deltoid really does appear externally, and we discovered another with the same 

 peculiarity in the National Collection. We were quite inclined to agree with 

 Hambach in regarding this as an anomalous development until we received a letter 

 from Mr. Wachsmuth, in which he expressed his belief that the deltoid of the anal 

 side always appears externally in this manner so as to truncate the two subjacent 

 radial limbs ; while the other four deltoids are not visible externally, the interradial 

 sutures extending right up to the summit, as shown in our PI. XII. fig. 11. 



Mr. Wachsmuth's letter was accompanied by five specimens, two of which certainly 

 bear out his statement, while the condition of the other three is not such as to enable 

 us to speak decisively about them. But on reinvestigating the three examples of 



1 Ibid. 2 ' Canadian Naturalist,' 1881, vol. x. no. 2, p. 82. 



8 Proc. Davenport Acad. Nat. Sci. 1885, vol. iv. p. 80. 



4 Archiv f. Naturgeseh. 1851, Jahrg. xvii. Bd. i. p. 373, tat', iii. figs. 12 a, 12 6. 



6 'Die Silurischc Fauna des westlichen Tennessee,' Breslau, 1800, p. 60, taf. iii. figs. 2 a, 2c. 



" Trans. St. Louis Acad. Sci. 1S84, vol. iv. no. 3, p. 540. 



