TUNICATA 671 



plex branching systems of small size, with body composed of 2 portions ; 

 incurrent opening 6-lobed : 9 genera, with numerous species. 



DIDEMNUM Girard. Colony usually thick, opaque, often leathery; 

 calcareous spicules stellate in form; zooids small, with 3 rows of stig- 

 mata in the branchial sac: numerous species. 



D. orbiculatum Van Name. Colonies thin, 25 mm. wide and 2 mm. 

 thick, gray in color, with numerous spicules which tend to conceal the 

 zooids: common on the underside of stones near low water in Bermuda. 



D. lutarium Van Name (Leptoclinum albidum Verrill; L. luteolum 

 Verr.). Colony forms a thin incrustation up to 30 cm. in diameter, cov- 

 ering stones, shells, etc., and white or pink in color, with an uneven 

 surface by reason of the numerous calcareous spicules present: Long 

 Island Sound to Labrador; common; in shallow water. 



ORDER 3. ASCIDIAE LUCIAE.* 



Animals colonial, free-swimming, and enclosed in a common tunic; 

 colony cylindrical, conical or flattened in shape with one open end; 

 zooids arranged in a single layer, perpendicular to the surface, the incur- 

 rent openings being on the outer and the 

 cloacal openings on the inner surface of 

 the cylindrical colony; projecting from 

 the outer surface are often long finger- 

 like processes of the tunic, and at the 

 forward end of the branchial sac of each 

 zooid are paired phosphorescent organs; 



the colony swims with the closed end in Fig. 1,015 Pyrosoma, atlanticum 



(Cambridge Natural History), 

 advance as the result ot the streaming 



of water out of the open end: 1 genus, the species of which are noted 

 for their brilliant phosphorescence. 



PYROSOMA Peron. With the characters of the order; colony 

 cylindrical or flattened : 8 species, in tropical seas. 



P. atlanticum Per. (Fig. 1,015). Colony conical, 3 or 4 cm. in 

 diameter, and 25 cm. or more in length, although usually much smaller; 

 color greenish, pinkish, or yellowish: in the tropical Atlantic. 



SUBPHYLUM 3. LEPTOCARDIA.* ( CEPHALOCHOKDATA ; 



AMPHIOXUS.) 



Elongate, fish-shaped Chordata, in which the notochord extends the 

 entire length of the body. The body is laterally compressed and pointed 



* See "Cyclomyaria et Pyrosomida," by G. Neumann, Das Tierreich, 1913. 

 t See "Amphioxus and the Ancestry of Vertebrates," by A. Willey, 1894. "A 

 Revision of the Genera and Species of the Branchiostomidae," by J. W. Kirkaldy, 



