78 PROCEEDINGS OF THE ACADEMY OP [1886. 



radial of the posterior side is quadrangular, and supports a longi- 

 tudinal row of anal plates, which extend to the full length of the 

 calyx, and in their form closely resemble the radials. Arms 

 apparently recumbent. Column more or less obtusely pen- 

 tagonal ; axial canal large. 



Geological Position, etc. Lower Silurian, Canada. No addi- 

 tional species have been described. 



SuBORDEK INADUNATA. 

 a. Branch, Larviforviia. 



The Larviformia comprise the families : Haplocrinidse , Sym- 

 hathocrinidse, Gupressocrinidee and Gasterocomidse. 



The Haplocrinidse are the simplest brachiate Crinoids and 

 may be regarded as representing the larva, not only of the 

 Inadunata but of the Palaeocrinoidea generally. Even the most 

 complicated Platycrinoid or Actinocrinoid must have passed in 

 its early life a stage in which radials and interradials consisted of 

 but a single ring of plates when we think the interradials covered 

 the entire ventral surface. This stage is probably represented by 

 the young Allagecrinus. In Haplocrinus the conditions are essen- 

 tially the same, but here the interradials already began partly to 

 open out, and the oral plate made its appearance upon the surface. 

 It is very possible that also the growing Allagecrinus before 

 reaching maturit}' attained this condition, or perhaps even the 

 condition of Symbathocrinus, hut in default of any such evidence, 

 we refer the genus for the present to the Haplocrinid?e. 



The Haplocrinidse are very closely allied to the Sj'mbatho- 

 crinidse, and it is a question with us, whether it would not be 

 better to unite them under one family. Both are built essentially 

 on the same plan, but the S3'mbathocrinidie at least their 

 typical genus had proximals, and, as a rule, a somewhat higher 

 developed mode of articulation. The articular facet in the 

 Symbathocrinidae forms a straight horizontal line, it is extended 

 into a large muscle-plate, and this covers the greater part of the 

 ventral cavity, leaving only a small median space, which is covered 

 either by the interradials and an oral plate as probably in Fiso- 

 crinus, or by interradials and a full set of summit plates as in 

 the case of Symbathocrinus. In the Haplocrinidse the inter- 



