86 ZOOLOGY. 
Silurian Heliolites, form, according to Moseley, a new 
family of Alcyonarians in which the corallum consists of an 
abundant tubular conenchym, 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 cceonenchy- 
mal tubes are closed with a layer of soft tissue, but com- 
municate with one another and with the calicular cavities 
by asystem of transverse canals (Moseley). Heliopora ceru- 
lea grows on coral reefs at the Philippine Islands and at 
Singapore. 
In the family of sea-fans (Gorgonide) 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. Gorgonia (Rhipigor- 
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. George’s Banks, 
Primnoa reseda (Pallas) and Paragorgia arborea (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 (Pennatulide) 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 Pennatula, or the sea-pen, there are secondary 
branches in which the polyps are situated ; this polyp is 
phosphorescent ; one species (P. aculeata Danielssen) lives 
in deep water. An Arctic form, Umbellularia groenlandica, 
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, 8. 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, 
