The brilliant phosphorescence of many species of Pennatulacea has been observed by many naturalists, and it is very probable that they all exhibit this property to some degree. The phosphorescence appears to be emitted by the mesenteric filaments of the autozooids, but it is not yet determined whether the phenomenon is confined to these organs or is more generally distributed. The Pennatulacea are usually devoid of epizoites, but occasionally the parasitic or semi-parasitic Entomostracan _Lamippe_ is found in the zooids. A small crab is also frequently found between the large leaves of species of _Pteroeides_. The most remarkable case of symbiosis, however, has recently been observed in the form of an encrusting Gymnoblastic Hydroid[390] living on the free edge of the leaves of a species of _Ptilosarcus_. The order Pennatulacea is divided into four sections. SECT. 1. PENNATULEAE.—In this section the colony is distinctly bilaterally symmetrical, and the autozooids are arranged in rows with their body-walls fused to form leaves. The genus _Pteroeides_, the representative genus of the family PTEROEIDIDAE, is a fleshy Sea-pen found in shallow sea water in the warm waters of the Pacific Ocean and in the Mediterranean. It has large leaves with long spiny, projecting spicules, and the siphonozooids are borne by the leaves. _Pennatula_, the representative genus of the family PENNATULIDAE, has a wider distribution in area and in depth. _Pennatula phosphorea_ is a common British species, found in depths of 10 to 20 fathoms in many localities off our coasts. It is about 5 inches in length. There are several varieties of this species distributed in Atlantic waters. _Pennatula grandis_ is a magnificent species found in Norwegian fjords, in the Faeroe Channel, and off the northern coasts of N. America, in depths of from 50 to 1255 fathoms. Specimens have been {362}obtained no less than 2½ feet in length. _P. murrayi_ and _P. naresi_ are species of the genus found at depths of a few hundred fathoms in tropical seas. The genus _Virgularia_, belonging to the family VIRGULARIIDAE, is represented in the British seas by _V. mirabilis_, a long slender Sea-pen found in many localities off the Scottish coasts. SECT. 2. SPICATAE.—This section includes those Sea-pens in which the autozooids are arranged bilaterally on the axial zooid in rows or more irregularly, but do not unite to form leaves. It is a large section and contains many widely divergent genera. The family FUNICULINIDAE is represented on our coasts by _Funiculina quadrangularis_, a long and slender Sea-pen 2 to 3 feet in length. The autozooids are arranged in oblique rows, and the siphonozooids are on the ventral side of the rachis. There is one point of special interest in this genus. The siphonozooids appear to change as the colony grows and to become autozooids. If this is the case it may be more correct to describe the genus as devoid of true siphonozooids.