Hambach — Revision of the Blastoideae. 3 



structiou of Echinodermata are arranged in multiples of five 

 around a central axis. However, deviations from the preva- 

 lent rule occur more frequently in this class of the animal 

 kingdom than elsewhere. Such abnormal developments have 

 often been the cause of redescribiug well-known forms as 

 new species, especially among the Crinoideae.* For the 

 purpose of illustrating the tendency of abnormal develop- 

 ments I will give a few examples, which, however, I could 

 have multiplied if time and space would permit. Similar de- 

 formities have been observed and described by others. f In 

 Fig. 13 and 14, Plate III., we have a specimen of Pentremites 

 Jlorealis, with only four fork pieces and four ambulacra. 

 In Fig. 8 and 9, same plate, Pentremites pyinformis has four 

 ambulacra but five fork pieces, of which the fifth is not 

 fully developed. Fig. 15 and 16, same plate, Pentremites 

 pyriformis, show six fork pieces but only four ambulacra 

 are fully developed. Fig. 11 and 12, same plate, Pentremi- 

 tes sidcatus, show five fork pieces, one of which is a 

 longitudinal square without any sinus, and consequently 

 no ambulacrum has been developed. In Fig. 10, same plate, 

 Pentremites sulcatus, we have one ambulacrum developed only 

 to one-half the length of the others. Fig. 6 and 7, same 

 plate, Pentremites sulcatus, show an extra longitudinal piece 

 inserted between two fork pieces. Fig. 18, same plate, Pen- 

 tremites Jlorealis, has only four fork pieces but five am- 

 bulacra, so that two ambulacra are inserted into one sinus, 

 causing the two opposite halves of the ambulacrum to form 

 a prominent ridge. In Fig. 17, same plate, Pentremites 



* See Bulletins of the Illinois State Museum of Natural History, by S. 

 A. Miller and W. F. E. Gurky, Nos. 1-12. 



t Robert Etheridge, Jun., and P. Herbert Carpenter. Catalogue of the 

 Blastoidea. 



Hermann von Meyer. Abweichung von der Fiiufzahl bei Echinideeu. 



Prof. Georg Boehm. Ueber eine Anomalie im Kelche von Millericrinus 

 mespiliformis . Zeitschrift der deutschen geologisclien Gesellschaft. Band 

 XLIII., Hefts, p. 741. 



H. W. Mackintosh. On a Malformed Corona of Echinus esculentu^. 

 Proceedings of the Royal Irish Academy. Vol. II., Ser. II , 1875, p. 206. 



Dr Pliillppi. Beschreibung zweier mis.sgebildeter See-Igel. Wiegmaun's 

 Archiv liir Nalurgeschichte. Band I., 1837, p. 241. 



