340 BIOLOGICAL SURVEY OF 



MucRONELLA vENTRicoSA (Hassall), 1842. PI. 15, figs. 7 and 

 9b. (Osbiirn, 1912, p. 243, for references; Whiteaves, 1901, 

 p. 107, for Canadian records.) Common on shells and stones, 

 on hard bottoms ; taken at twenty-one dredging stations, not 

 found at shore stations. Abundant in northern seas, prob- 

 ably circumpolar, on the American coast occurring from 

 Greenland to Cape Cod. The frontal surface of the zooecium 

 is swollen, smooth, or minutely granular in radiating rows. 

 A row of small marginal pores is present, and a conspicous 

 double-pointed tooth occupies the middle of the proximal bor- 

 der of the rounded aperture. A projecting umbo often ob- 

 scures this tooth from above. The ooecium is conspicuous, 

 globular, and imperforate. 



MucRONELLA ABYssicoLA (Normau), 1868. PI. 15, figs. 8- 

 9 c. (Wliiteaves, 1901, p. 107, Canadian records.) Rare, 

 dredged at stations 52 and 62 on pebbles. An Arctic and 

 North Atlantic species, Spitzbergen and Greenland and south- 

 ward nearly to Cape Cod. The zooecia are swollen, broadest 

 at the middle and somewhat tapered at both ends, separated 

 by deep fissures. The aperture is comparatively small, con- 

 siderably broader than long, with a very broad denticle on 

 the proximal margin. The denticle is overhung by a broad 

 flattened umbonate process, which in fertile zooecia is often 

 continued around the sides of the aperture to meet the ooecium 

 and form a spout-like peristome. The ooecium is of moderate 

 size, globose, broader than long, and minutely granular like 

 the frontal surface. Two or three short spines are often 

 present on the oral border. 



Mtjcronella spinulifera Hincks, 1889. PI. 15, fig. 10. 

 (Hincks, 1889, p. 431, pi. 21, fig. 3; 1892, p. 152 (Monoporella), 

 Gulf of St. Lawrence ; Whiteaves, 1901, p. 108 (Monoporella) ; 

 Osburn, 1912 a, p. 282, Labrador.) Rare, noted only once, a 

 small colony on a pebble at dredging station 62. An Arctic 

 and North Atlantic species which has been previously recorded 

 from Franz Josef Land, northern Norway, Greenland, and 

 south to the Gulf of St. Lawrence. 



