354 PROCEEDINGS OF THE ACADEMY OF [1888. 



in the Palaeocrinoids there are many families in which the articular 

 facet of the first radial simply occupies the middle of its distal edge,- 

 but this is not the case with the Ichthyocrinidea, the most of the 

 Poteriocrinidae, Cupressocrinidse, and Symbathocrinidae. 



The main point, upon which Etheridge and Carpenter/ and after- 

 wards Carpenter aloue,'^ distinguished the two groups was stated to 

 be the regularly pentamerous symmetry of the calyx in Neocrinoids 

 contrasted with the asymmetry of the Palaeocrinoids, in which " the 

 pentamerous symmetry of the calyx^ is almost always disturbed by a 

 greater or less modification of the plates on the anal side. " From 

 this Carpenter was obliged to except the genus Thaumatocrinus, as to 

 the Neocrinoidea, which has well developed anal plates. 



A far greater number of exceptions are found in the Palaeocrinoidea, 

 among the Camarata as well as the Inadunata and Articulata. 

 Among the first may be mentioned Dolatocrinus, Stereocrinus, Centro- 

 crmus, Technocrimis, Corymbocrinus,Eucalyptocrinusand Callicrinus, 

 in which the anal interradins cannot be distinguished in the dorsal 

 cup from the four others; Lyriocrinus, Ripidocrinus, Thylacocriims, 

 Rhodocrinus, and Gilbertsocriiius, in which it is rarely distinct ; and 

 Briaroatnnus whose irregularity is not caused by anal plates. Among 

 the Inadunata there are Codiacrinus, Lecythiocrinus, Stemmatocrmus 

 and Erisocrinns, in none of which the usual anal plate is known to 

 exist. Among the x4.rticulata, we note Ichthyocrlnus and Niptero- 

 crinus as being in a similar condition as Briarocrinus. In some of 

 the above genera, however, there is an ii-regularity in the basals; yet 

 this is not due to anal plates, but to a coalescence of two or more 

 of the plates, a variation which is also found in the recent genus 

 RJiizocrinus, and among the underbasals in the Antedon larva. 



i"On Allagecrinus, Ann. and Mag. Nat. Hist., Apr. 1881, pp. 295 and 

 296. 



2 Challenger Report on Stalked Crinoids, p. 150. 



3 It must be observed that the term " calyx " was used by Dr. Carpenter in the 

 Challenger Report, and by us at that time, to designate the part of the test below the 

 arm bases. Findmg more and more the necessity of having a more stable terminol- 

 ogy, which would be applicable to the Crinoids generally, we have agreed with Dr. 

 Carpenter upon the following terms, which will be used by both of us hereafter for 

 descriptive purposes, viz : — 



Crmoid minus the stem = Crown. 



Crinoid minus stem and arms = Calyx. 



All parts of the calyx below the arm bases := Dorsal cup. 



The ventral perisome with mouth and ambulacra = Disk, 



All parts covering the disk ^ Vault. 



