BRYOZOA OF WOODS HOLE REGION. 251 



4. Erect branches rather firm, the gelatinous substance comparatively solid, zooecia closely packed, 



tentacles about 10 in number -verrilli. 



Branches softer, the gelatinous matter comparatively soft, zooecia not so closely packed, tentacles 

 15 to 17 in number gelatinosum. 



Alcyonidium parasiticum (Fleming). [PI. xxvn, fig. 73.] 



Fleming 1828, p. 518 (Alcyonium parasiticum). 

 Verrill and Smith 1874, p. 708. 

 Verrill 18790, p. 28. 



Zoarium encrusting on stones, shells, and stems of various sorts, impregnated with earthy matter 

 which gives the colony the appearance of a coating of mud. The zooecia, which are rather small, appear 

 in the midst of this layer as depressed areas with minute papillae around the border. In the younger 

 parts of the colony the zooecia project somewhat and the septa are evident. The tentacles are about 

 15 in number. 



Verrill records this species from Vineyard Sound at a depth of a few fathoms. It was not noted in 

 the inner waters of the region during our survey, but was taken at Crab Ledge in 14 to 20 fathoms, and 

 off No Mans Land in 29 fathoms, in considerable abundance. It has not been reported from Canadian 

 waters, but occurs on the European coasts. 



Alcyonidium mytili Dalyell. [PI. xxvm, fig. 74, 74a.] 



Dalyell 1847, p. 36. 



Verrill i879b, p. iSS (Alcyonidium rubrum, n. sp.); 18790, p. 28 (as A. mylili and rubrum). 



Zoarium encrusting on stones and shells, occasionally on seaweed, forming rather firm, dingy white, 

 yellowish, reddish, gray or brown colonies, sometimes quite dark, at other times almost colorless, 

 covered with small, low prominences when the zooids are retracted. Zooecia typically hexagonal, but 

 this form is often modified to a pentagon or quadrilateral; septa showing with more or less distinctness 

 on the surface. 



Hincks (1880) says of this species that the ova are borne in special zooecia destitute of polypides, 

 within which the ova are arranged so as to form a ring. This is not entirely true of our specimens, for 

 the eggs are most certainly developed in the ordinary type of zooecium. I have counted as many as 

 14 developing embryos within a single zooecium, though the number varies greatly and not infre- 

 quently there are only one or two; when numerous they may be arranged in a circle. I am inclined 

 to think that the polypide may degenerate as the embryos approach maturity, thus giving the appear- 

 ance of a special zooecium. There is more than a possibility that the A . polyoumoi Hassall (1841, p. 484, 

 Sarcochitum polyoum) may be the same species, as there seems to be little except the arrangement of 

 the ova to distinguish it from mytili. In this case Hassall 's name will have precedence. 



I believe I am correct in identifying Verrill's rubrum with mytili. Certainly I have taken the 

 brick-red form, which I have not been able to separate structurally from the pale and grayish-brown 

 specimens, which I have compared with British specimens of mytili. Verrill's description is as follows: 

 "An encrusting species, forming broad smooth colonies, covering stones and shells. Zooecia rather 

 large, mostly hexagonal, but often pentagonal, with their boundaries well marked in alcoholic speci- 

 mens by a distinct line. The retracted zooids in preserved specimens usually form a small papilla in 

 the middle of the zooecia. Color in life, bright brick-red, or sometimes orange red. ' If further study 

 shall prove that the arrangement of the ova and their method of development in a distinct form of 

 zooecium is characteristic of mytili, then rubrum must stand as a distinct species, but certainly there is 

 nothing distinctive in the color or the general character of the zooecia. 



Widely distributed over the region, from low water to 16 fathoms, sometimes forming extensive 

 crusts on piles, taken also on barnacles, skate egg cases, on the carapace and legs of crabs (especially 

 Libinia) and occasionally even in the branchial chamber, as well as on stones and shells. Verrill 

 records rubrum from Long Island to Nova Scotia. 



