BRYOZOA OF WOODS HOLE REGION. 247 



globose, large, in young state shining and pierced by large irregular punctures, in older stages the pores 

 may become closed and the surface roughly granular. 



Although Hincks, Waters, and McGillivray have considered this a separate species, I have no 

 hesitation in ranking it merely as a variety of the extremely variable trispinosa. My reasons for so 

 doing are as follows: First, the characters of the zooecial wall, primary orifice, peristome, spines, and 

 ooecium are identical in both, and uitida runs through all the variations due to calcification that are 

 shown by trispinosa. Second, the avicularia intergrade to such an extent that it is impossible to draw 

 a dividing line; nitida has usually only the small oval avicularia, but larger spatulate avicularia are not 

 uncommon and are sometimes abundantly developed, and in addition to these specimens are occasion- 

 ally found, otherwise undistinguishable from nitida, which have the large pointed avicularia exactly 

 similar to those of trispinosa, while on the other hand specimens of trispinosa from Crab Ledge have 

 spatulate avicularia of various lengths showing the transition from the small oval form usually present. 

 In size the zooecia also intergrade completely. I therefore regard nitida as a variety of trispinosa in 

 which the large, pointed avicularia are wanting, while the oval and spatulate forms are more plentifully 

 developed. 



For comparison I have had specimens of trispinosa from England, Labrador, Nova Scotia, Beaufort, 

 N. C., and the Tortugas Islands, Fla. 



The variety nitida replaces the typical trispinosa in Vineyard, Nantucket, and Long Island Sounds, 

 Buzzards and Narragansett Bays, and other inshore waters of southern New England. It is extremely 

 abundant from low water to 20 fathoms, and is one of the characteristic Bryozoa of the region. It has 

 been reported also from the British Isles and from Australia, where, without doubt, it constitutes a 

 local form of the cosmopolitan trispinosa, as it does here. 



Genus PORELLA Gray, 1848. 



This genus may be recognized by the form of the zooecial aperture, rounded in front and nearly 

 straight behind, with a rounded avicularium mounted on a rostrum immediately behind the primary 

 orifice, which it usually overhangs somewhat. A shelf-like projection is present on the posterior margin 

 of the orifice in P. concinna (for which reason Jullien and Calvet have placed the species in the genus 

 Smittia), but otherwise the margin is plain behind and is never sinuate. The secondary orifice, formed 

 by the growth of the peristome, is entirely different in character, usually more or less pyriform, with 

 the pointed end posterior and including the aviculiferous rostrum in its sinus-like fold. Many species 

 of this genus are erect and branching in manner of growth, but all of ours are encrusting or rise merely 

 into low frills. 



KfiY TO SPECIES. 



1. Primary orifice with a broad shelf-like projection on the posterior margin concinna. 



Primary orifice without such projection 



2. Rostral avicularium with a somewhat pointed mandible directed upward acutirostris. 



Avicularium rounded 



3. Primary orifice large and somewhat rounded posteriorly, large spatulate avicularia often present in 



addition to the rostral one .propinqua. 



Posterior margin straight, rostral avicularia only; zoarium erected into frill-like expansions, proboscidea. 



Porella concinna (Busk). [PI. xxvn, fig. 67, 6ya, 6yb, 68.] 



Busk 1852, p. 67 (Lepralia concinna'). 

 Dawson 1858, p. 256 (Lepralia belli). 

 Stimpson 1853 (Lepralia rubcns). 

 Packard 1867, 271 (Lepralia belli). 

 Verrill 18790, p. 30 (P. Icnis var. concinna). 

 Hincks 1889, 428, 1892, p. 156. 

 Whiteaves 1901, p. 102. 

 Cornish 1907, p. 78. 



