36 ZOOLOGT. 



Silurian Heliolites, form, according to Moseley, a new 

 family of Alcyonarians in which the corallum consists of an 

 abundant tubular coenenchym, with calicles having an 

 irregular number of pseudo-septa, which do not, however, 

 correspond with the membranous mesenteries. The polyps 

 are completely retractile, with the tentacles when retracted 

 introverted. The mouths of the sacs lining the coenenchy- 

 mal tubes are closed with a layer of soft tissue, but com- 

 municate with one another and with the calicular cavities 

 by a system of transverse canals (Moseley). Ileliopora cceru- 

 lea grows on coral reefs at the Philippine Islands and at 

 Singapore. 



In the family of sea-fans (Goryonidce) the coral-stock is 

 horny or calcareous, branching tree-like, or forming a flat 

 network. The short calicles of the single retractile polyps 

 stand perpendicularly to the axis, communicating by longi- 

 tudinal vessels and branching canals. Gonjmiui (Rliipir/or- 

 gia) flabellum- Linn, is red or yellow and abundant on the 

 Florida reefs. In the Arctic seas and the deeper, colder 

 waters of the Newfoundland Banks and St. G-eorge's Banks, 

 Primnoa reseda (Pallas) and Paragorgia arborca (Linn.) 

 grow ; the latter being of great size, the stem as thick 

 through as one's wrist, and the whole corallum over five feet 

 in height. 



In the family of sea-pens (PennatulidcB) the polyp-stock 

 is free, growing in the sand or mud, usually with a bony 

 axis supporting the polyps, and capable of moving at the 

 base. In Peimatula, or the sea-pen, there are secondary 

 branches in which the polyps are situated ; this polyp is 

 phosphorescent ; one species (P. aculeaia Danielssen) lives 

 in deep water. An Arctic form, Umbellularia yroenlandica, 

 is a gigantic form, growing about four feet high, in from 

 three hundred to two thousand fathoms. The species of 

 Renilla are kidney-shaped, with the polyps placed on one 

 side. Renilla reniformis Cuvier is a rich purple species, 

 occurring in the sand at Charleston, S. C. According to 

 Agassiz, this animal is remarkably phosphorescent, emitting 

 *" a golden green light of a most wonderful softness." 



While coral reefs are in part composed of Alcyonarians, 



