272 PROCEEDINGS OF THE ACADEMY OF [1885. 



outside the ring of proximate. Yet such is the case in Megisto- 

 crinus Evansii and in Megistocrinus brevicornis, in which the 

 anal tube is extremely small, located beneath the arm regions, 

 and separated from the proximals by from ten to twenty rings of 

 plates. At the az} r gous* side they have two well-defined proxi- 

 mals, separated by irregular small plates, in a similar manner as 

 in other groups. If these pieces were orals, as asserted by 

 Carpenter, it is difficult to understand wh} r they should be divided 

 in these species, especially if we take into consideration that the 

 orals in all recent Crinoids, even in the asymmetrical Thaumato- 

 crinus, consist of five undivided plates. 



There is not a single instance known among recent Crinoids in 

 which the anal opening penetrates the orals, not even in the early 

 larva, in which the oral pyramid occupies the whole ventral sur- 

 face. In the larva the opening is placed within the equatorial 

 zone, beneath the orals, and the same is probably the case in 

 Hoi opus, in which the orals retain permanently the condition of 

 the larva. In the more advanced stages, the anal opening is 

 carried inward by the gradually increasing perisome, but it 

 remains outside the oral ring in all cases, whether the orals 

 become absorbed as in Pentacrinus, Bathycrinus and Antedon, or 

 are retained permanently as in Rhizocrinus, Thaumatocrinus 

 and Hyocrinus. 



In the face of such evidence it seems to us extremely hazardous 

 to assert that in Palaeozoic Crinoids the anus penetrated the orals, 

 or was closely connected with them. But we must make this 

 assertion if we are to accept the interradials in Haplocrinus, and 

 the so-called proximals in other genera, as the representatives of 

 the orals. We might account for a slight disturbance in the form 

 of the plates in genera in which the anus, or its component parts, 

 come in direct contact with the plates, 1 but in our opinion no 

 explanation whatever can be given why in such forms as Megisto- 

 crinus, Grotalocrinus, etc., the posterior oral plate should be 

 divided. For the same reason we cannot accept the five inter- 

 radial plates in Haplocrinus to be orals. If Haplocrinus was in 



1 There is a case in which the anus penetrates the central piece. In the 

 Calyptocrinidse in which the whole calyx — with the exception of the 

 basals— is symmetrical, the anus is strictly central, and the proximals com- 

 pletely pushed out of position, the central piece is bisected, and the two 

 halves, jointly with the proximals, form the sides of the anal tube. 



