SUBORDER ALCYONARIA. 587 



(see p. 123). The coralla are sometimes tubular, and when so, the tubes 

 are peculiar in being smooth within, without lamellar rays or stria3. 



The Alcyonaria differ in being either free (or simply buried at base), 

 or attached by growth. The former species constitute the family 

 PennatuUda, and the latter the remaining families. It may be ques- 

 tioned, however, whether this distinction should not require the insti- 

 tution of the two groups as equivalent tribes. The attached species 

 form either tissue-secretions alone, or separable foot and tissue-secre- 

 tions. These last are the Gorgonidce ; the others, when the coral 

 secretions are disseminated grains or spicules, belong to the family 

 AlcyonidcB ; and when they form tubular coralla, to the families Cor- 

 ni//'iridce and Tubiporidce. These families may be briefly charac- 

 terized as follows : 



1. PENNATULID^;. Free, or with the base buried. 



2. ALCYONID.E. Attached ; no coral secretions, or only calcareous 

 spicula within, and no axis. 



3. CORNULARID^E. Attached ; coralla tubular, corneous. 



4. TuBiPORiDvE. Attached ; coralla tubular, calcareous. 



5. GORGONID^E. Attached ; a separable axis to the branches. 



FAMILY L-PENNATULID.fi. 



Alcyonaria nunquam ajfixa, sive libera sive bast defossa. 

 Unattached Alcyonaria, either free or with the base buried. 



These zoophytes are either flat plates, simple stems, or plume-like 

 fronds. The polyps occur on one or both sides of the stem or branches, 

 and in a single genus form a cluster at the extremity. The base of 

 the zoophyte is often somewhat enlarged, and some species, by means 

 of it, are planted in the mud. The greater part of them secrete a 

 slender solid axis along the main stem or midrib of the frond, which 

 is either cartilaginous or calcareous. The polyps have the o-eneral 

 characteristics of the Alcyonia. 



