Fig. 18. Colonies of _Ascidiæ compositæ_, natural size. A. _Colella quoyi._ B. _Leptoclinum neglectum._ C. _Pharyngodictyon mirabile._ D. _Botryllus._ (After Herdman, _Challenger_ Report and Encyclopædia Britannica.) ] _Julinia ignota_, from the Antarctic regions, forms long narrow colonies, which attain a length of nearly three feet. One end is attached, the rest of the colony apparently lying along the sea-bottom. _Amaroucium roseum_ from Naples forms translucent gelatinous masses; a slice is exhibited, showing the long slender ascidiozooids immersed in the mass. [Illustration: Fig. 19. _Pyrosoma elegans_, natural size. A. Side view of entire colony. B. End view of open extremity. (Herdman: _Tunicata_, Encyclopædia Britannica.) ] _Pharyngodictyon mirabile_ (Fig. 18 C), from 1600 fathoms in the Southern Indian Ocean, resembles a small mushroom, and is about one inch in height. This species is one of the few deep-sea Compound Ascidians. _Leptoclinum albidum_ is a common and widely distributed species; it occurs in the form of thin white crusts. The glistening white appearance is due to the common test being densely crowded with minute stellate spicules of carbonate of lime. The specimen of _Leptoclinum neglectum_ (Fig. 18 B) encrusts a fragment of sponge. _Goodsiria pedunculata_ from the Straits of Magellan, forms a rounded cartilaginous mass attached by a short peduncle; sometimes several masses are attached to each other. Each of the small dark oval areas on the surface corresponds to the branchial and atrial orifices of one ascidiozooid. _Sub-order 3._—ASCIDÆ SALPIFORMES. The Salpiform Ascidians comprise only one genus, _Pyrosoma_, which occurs in the form of free-swimming colonies shaped like hollow cylinders closed and rounded at one end and open and truncate at the other (Fig. 19). The wall of the cylinder is formed of a single layer of ascidiozooids (Fig. 20), so arranged that all the atrial orifices open into the interior of the cylinder, and all the branchial orifices on the exterior, the two kinds of orifices being at opposite ends of the body, and not close together, as in most simple and compound Ascidians. Specimens vary in size from a few inches to upwards of four feet in length, and, as the name of the genus implies,[22] they are brilliantly phosphorescent. Sometimes they occur in innumerable multitudes, giving rise to a zone of greenish light extending for miles. Professor Moseley records that during the voyage of the _Challenger_ in the North Atlantic a huge specimen of _Pyrosoma spinosum_, four feet in length, was captured. On tracing his name on its body, the word came out in letters of fire. [Illustration: Fig. 20. Section through wall of _Pyrosoma_, magnified, showing a single layer of ascidiozooids. _br_, branchial; _at_, atrial orifice; _tp_, process of the test; _br s_, branchial sac. (Herdman: _Tunicata_, Encyclopædia Britannica.) ]