ZOOLOGICAL EH8TORT OF THE BLASTOIDEA. 3 



respectively. These are all well-defined generic typos, and have been since recognized 

 as valid. But in 1849 D'Orbigny ' established the genus Pentremitidea for two 

 Spanish Blastoidsin which he supposed deltoid pieces to lie absent. Roemer 2 showed, 



however, that D'Orbigny was hero in error; and the genus consequently fell into 

 disuse till it was revived by ourselves in 1882 with a more precise definition :; . 



During the first half of the present century the morphology of the Blastoids seems 

 to have attracted but little attention. Roemer ' discovered the so-called pinnules of 

 Pentremites in 1848; and two years later Owen and Shumard s announced the dis- 

 covery of Pentremites with the summit-opening closed by plates. Except in these 

 points, however, hardly anything was added to our knowledge of the morphology of 

 the Blastoidea, Goldfuss (the chief German palaeontologist) being led astray by their 

 supposed resemblance to the Echinoidea ; while the descriptions of new genera were 

 of the most superficial nature, with scarcely any foundation of anatomical facts. 



In the year 1 S 5 "J , however, all this was changed by the publication of Roemer's 

 classical monograph G of the Blastoidea, and of the Pentremites in particular. 

 Several new species of this genus were described and the existing ones re-defined ; 

 while it was divided into four sections, each with its typical species. The careful 

 discrimination exercised by Roemer in this classification is strikingly manifested 

 by the fact that each of the specific types employed by him in this way is now 

 regarded as representing a distinct genus ; while three other genera have been 

 established for the reception of species such as Pentremites car//ophrjt!«t/rs,'DeK.onmck, 

 P. obtiquatus, Roemer, sp., and P. ycntanijidaris, Miller, sp., which were respectively 

 placed by Roemer in the first three sections of the genus, but with a " query" attached 

 in each case. Roemer further gave an elaborate diagnosis of a very remarkable type, 

 Elceacrimts, which had been distinguished by both Conrad and Troost as generically 

 distinct from Pentremites, though neither author had ever given a proper description 

 of it. 



Important, however, as was Roemer's contribution to the systematic arrangement 

 of the Blastoidea, it was altogether eclipsed by his great additions to our knowledge 

 of their morphology. He gave a careful analysis of the three groups of plates 

 forming the calyx of a Blastoid, and was the first who clearly showed the relation 



1 C'ours elementaire de Paleontologie et tie Geologic stratigraphiqne. 1852, vol. ii. p. 139. 



- Archiv f. Xaturgeseh. 1851, Jahrg. xvii. Bd. i. p. 369. 



■' "On certain Points in the Morphology of the Blastoidea, with Descriptions of some new Genera and 

 Species." Ann. & Mag. Nat. Hist. 1882, vol. ix. p. 220. 



1 ■• Teller gegliederte, ana Kalkstiickchen zusammengesetzte Tentakeln odcr Pinnuhe auf den sogenanntrii 

 Amtralacral-Felderrj der Pentremiten." Neues Jahrb. f. Mineral. 1848, pp. 292-29G. 



5 '-Descriptions of Fifteen new Species of Crinqidea from the Sub-Carboniferous Limestone of Iowa. 

 Collected during the U.S. Geological Survey of Iowa, Wisconsin, and Minnesota in the years L848-49." 

 Journ. Acad. Nat. Sci. Philad. 1850, vol. ii. part 1. p. 65. 



6 Archiv f. Nafcurgesch. 1851, Jahrg. xvii. Bd. i. pp. :!2:'. :'.!>7. Taf. i.-v. 



B 'I 



