4 CATALOGUE OF THE BLASTOIDEA. 



of the so-called deltoid plates to the summit-openings ; while he laid the foundation 

 of a scientific study of the various ambulacral structures, and discovered the remark- 

 able complex organs which lie beneath them, now generally known as the hydrospires. 

 There can be little doubt, too, that he was correct in assigning a generative function 

 to this apparatus and to the summit-openings, though it is probable that they had 

 other functions as well. 



Roemer concluded with a reference to the systematic position of the Blastoidea. 

 Although he placed them in the order Crinoidea, he recognized, as Say 1 had pre- 

 viously done, that they agree with the Cystids and differ from the true Crinoids in 

 the absence of arms. Unaware of the excellent name " Pelmatozoa " proposed by 

 Leuckart 2 four years previously for the three groups of stalked Echinoderms, Roemer, 

 like many other naturalists, extended the name Crinoidea to include the armless 

 forms ; and, regarding it as of ordinal value, he considered the Blastoids, Cystids, 

 and Brachiate Crinoids as equivalent families or sections of the order. The prin- 

 ciples of Roemer's classification have been very generally adopted both in this 

 country and abroad ; but, owing to the elevation of the Echinoderms to the rank of 

 a subkingdom, the groups which he considered as families are now regarded as 

 classes or orders. There is some doubt, however, as to whether the Blastoids and 

 Cystids are in reality sufficiently distinct to rank as separate classes, for a large 

 number of apparently intermediate forms have been discovered during the thirty 

 years since Roemer wrote. The fundamental differences between Pentrcmitcs and 

 Echinosphcerites stand out even more clearly now than they did in 1850 ; but, on the 

 other hand, it is difficult to assign a definite position to Hybocystites and to some 

 other types of which Roemer knew nothing. 



A short time before the appearance of Roemer's Monograph, Owen and Shumard 3 

 published descriptions of four new species of Pentremitcs from the Carboniferous 

 Limestone of Iowa, U.S. One of these was founded upon an internal cast, as to the 

 generic position of which there must naturally be a good deal of doubt, but the 

 other three are now recognized as representing different genera, viz. Granatorrinus, 

 Cryptollastus, and Orophocrinus. 



In the year 1854 was published the classical memoir of De Koninck and Le Hon 4 

 upon the Carboniferous Crinoids of Belgium, among which they included five so-called 

 Pentremites. Three of these are now ranked with Orophocrinus and another with 



1 Journ. Acad. Nat. Sci. Philad. 1825, vol. iv. pt. 2, p. 292. 



2 Ucber die Morphologic und die Verwandtsehafta-Verhaltnissc dcr wirbellosen Thierc. Braunschweig, 

 1848, p. 12. 



* Journ. Acad. Nat. Sci. Philad. 1850, vol. ii. pt. l,p. 64. Reproduced, with additions, as " Descriptions 

 of one new Genus and twenty-two new Species of Crinoidea from the Subcarboniferous Limestone of Iowa," 

 Report Geol. Survey Wisconsin, Iowa, and Minnesota, 1852, pp. 587-598. 



4 " Recbcrches sur les Crinoides du Terrain Carbonifuro do la Belgiquc." Mem. Acad. Roy. Belgiquc, 

 1854, Mem. 3, pp. 189-204, 



