1890.] NATURAL SCIENCES OF PIIILADKLPnrx\. 373 



and the food grooves are roofed over by covering ])late.s, which were 

 ui)pareiitly iiniuoval>le. Tlie inouth was probably closed in all of 

 them. 



In tlie recent Holojyus, Hyocrhms and Bathycrinus, the ventral 

 sac is further reduced, so as to be a mere proboscis or anal tube. In 

 all of them the interambulacral plates them.selves are perforated 

 and not merely their margins, and mouth and food grooves are ex- 

 ])osed. 



The Inadunata Larvifonnia, as now restricted, have neither inter- 

 radial nor interambulacral plates, and rarely anals, and their orals 

 cover the ambulacra to the bases of the arms. They have apparent- 

 ly no water pores, in the calyx, and it is very possible that through- 

 out this group water for respiration was introduced through pores at 

 both sides of the arm ambulacra, as suggested already by us (Re- 

 vision, Pt. Ill, p. 83). 



The Articulata, the third great division of the Crinoidea, to which 

 we have heretofore referred only the Ichthyocrinidae, will probably 

 have to be amended so as to include the Comatulidae, Pentacrinidae, 

 Apiocrinidae and Bourgueticrinidae. How closely the Comatulidae 

 are related to the Ichthyocrinidae may be seen by comparing the 

 simpler forms of the latter with the young Antedon in its pedun- 

 culate state (Cliall. Report on Comat., PI. XIV). The stem in fig. 

 3 is exactly like that of Mespilocrinus, fig. 9 might represent as well 

 a young Onychocrinus, and the brachials of fig. 5, in their wav- 

 ing sutures are quite characteristic of the Ichthyocrinidae generally. 

 In all of these families the proximal brachials are incorporated into 

 the calyx, either by supplementary plates, by soft tissues, or by 

 sutural union. ^ In some species of the Apiocrinida? and Ichthy- 

 ocrinidae these supplementary pieces are quite large and massive, 

 and some have a sort of regularity in their arrangement, but they 

 are notwithstanding perisomic plates. The ambulacra throughout 

 this group are tegminal, although the plates are frequently not readily 



1 In some specimens oi Millericrinus it appears in the fossil as if their brachials 

 might have been free from the radials up; but we doubt it, as the capacity of the 

 calyx is too small to have contained the whole of the visceral cavity, and it seems to 

 us more probable that the lower brachials were connected by small plates or soft 

 tissues. A lateral union of the brachials, such as we find frequently in the Apio- 

 crinidae, and which occurs also in the Ichthyocrinidae, has never been observed 

 in any of the Camerata at least not between costals or distichals. In some Actino- 

 trinidae sometimes the higher bracliials are laterally connected. 



