BRYOZOA OF WOODS HOLE REGION. 243 



Mucronella peachii (Johnston). [PI. xxvi, fig. 58, 58a.] 



Johnston 1847, p. 31S (.Lepralia peachii). 



Dawson 1859. p. 256 {Lepralia peachii). 



Verrill and Smith 1874, p. 714 (? Discopora coccirua). 



Verrill 1879b, p. 195. and 1879c, p. 31 (Escharoides coccinta'). 



Whiteaves 1901, p. 107. 



Zoarium encrusting on stones and shells and occasionally on algse, usually irregular in outline but 

 the cells arranged with considerable regularity. Zooecia rhomboid, not separated by raised lines or 

 deep grooves, rather flat above, surface in young cells smooth with a row of large pores around the margin; 

 raised ribs then appear between the pores, forming radiate grooves with the pores at the bottom, and, 

 finally,- with complete calcification, the original surface is completely covered and the pores may be 

 obliterated; primary orifice longer than wide, rounded anteriorly, nearly straight behind, with an 

 emarginate or bifid tooth, the lateral denticles well developed, peristome slightly raised, produced 

 behind into a mucro and with six slender oral spines. Ooecia globose, smooth, imperforate, prominent 

 at first, but later more or less immersed. Avicularia wanting. The variations are almost entirely due 

 to calcification. 



Vineyard Soimd; Muskeget Channel; Great Round Shoal; Crab Ledge, and off Sankaty Head; 

 dredged in 6 to 20 fathoms. \'errill records the species as ver>' abimdant in Vineyard Sound and 

 Quicks Hole, but the results of our survey indicate that it is not common except locally in the inner 

 waters of the Soimd. 



Mucronella ventricosa (Hassall). [PI. xxvi, fig. 59, 59a.] 



Hassall 1842. p. 412 {Lepralia veniricosa). 



Verrill 1879c, p. 31 (Escbaroides coccinta var. zentricosa). 



Whiteavcs 1901. p. 107. 



Zoarium encrusting, forming whitish or silvery patches, usually irregular in outline, with the 

 cells radiating in rather regular linear series. Zooecia large, usually regularly disposed, swollen and 

 vcntricose, separated by deep grooves, a scries of small areola; about the margin, the surface smooth 

 in very young cells but soon becoming granular with minute roimded tubercles, which are generally 

 arranged in radiating lines; primary aperture rounded in front, straight behind with a large bifid denti- 

 cle; peristome raised very high and spout-like, thin on the sides, behind rising into a broad and often 

 massive prominence which may or may not bear a rounded umbo at its apex; four stout oral spines are 

 present in the yoimg cell, generally curving over tlie aperture in the fertile cell, but usually lost as 

 the peristome rises. Ovicell nearly globose, not impressed in our specimens, the surface granular 

 when fully calcified. Avicularia absent. 



The species is easily distinguished from M. peachii by its much larger size (averaging about twice 

 as large), by its much more convex form, and b^' the mode of secondar)' calcification. It never becomes 

 flattened as in peachii; the grooves separating the zooecia are ^■e^y deep, and the peristome is raised 

 into an erect, almost tubular, form. The mucro is much broader than in M. peachii. 



Taken rather rarely at Crab Ledge, growing on stones and shells, at 14 to 20 fathoms. 



Mucronella pavonella (Alder). [PI. xxvi, fig. 60.] 



Alder 1864. p. 106 {Eschara pavonella). 

 Verrill 1879b. p. 19s, and 1S79C, p. 30. 

 WTiiteaves 1901. p. 107. 



Zoarium encrusting on stones and shells, or forming fan -shaped expansions on hydroid and other 

 stems. Zooecia large and regularly arranged, convex and areolated arotmd the margin, and rising 

 toward the orifice in the young cell, but soon becoming flat with a secondary calcified layer which 

 often closes the areolae, orifice ver>' large, rounded, with a small posterior tootli, which varies in shape, 

 but which is usually blunt; peristome thin, smooth, unarmed, and but slightly raised. Ooecia wanting. 

 Avicularia oval, somewhat raised, situated one on either side of the orifice and close to it, with the 

 mandible pointing forward. 



