34 ALLAN HANCOCK ATLANTIC EXPEDITION REPORT 



Canu and Bassler state that the frontal is "perforated by large tremo- 

 pores." This may be an error due to the conditions of fossilization, but 

 if it is true the recent specimens must belong to a different species in spite 

 of the agreement in all other characters. 



Distribution. — Station At528, the Gulf of Venezuela, several colonies 

 encrusting shells. 



Genus AIMULOSI A Jullien 1 888 



Aimulosia floridana, new species 



Plate 6, Fig. 3 



Zoarium unilaminar, encrusting, especially on shells where small 

 rounded colonies are formed. The largest colony observed is about 1 cm 

 in diameter. 



The zooecia are quite variable in size, length 0.25 to 0.40 mm, width 

 0,20 to 0.30 mm, sometimes nearly as wide as long; rather regular in 

 form and arrangement, more or less quadrate ; distinct with well-defined 

 interzooecial grooves in the younger stages. The frontal is a thick pleuro- 

 cyst, smooth and shining but becoming rougher with age; a single row 

 of areolar pores, separated by short costae; the front is elevateJ toward 

 the aperture. The peristome is considerably elevated proximally and the 

 secondary aperture slants distally ; the wall thick ; a strong umbonate 

 process rises above the proximal border of the aperture and often bears a 

 minute pointed avicularium on the side near its tip. The primary aperture 

 is subcircular, less rounded on its proximal border, slightly longer than 

 broad (0.10 mm long by 0.09 mm wide) ; four oral spines are present 

 in very young stages but soon disappear. 



An avicularium with an acute triangular mandible directed distally 

 is usually situated opposite the operculum ; not infrequently there is one 

 on each side and often they are both wanting. Rarely a similar avicu- 

 larium may be present on the front, usually near the proximal end. 



The ooecium is veiy prominent, short and wide (width 0.20 mm), 

 cucullate, thick walled, smooth and shining with sometimes a small 

 rounded boss at the top; very wide open and with the median border 

 curved slightly forward and downward. This t5^pe of ooecium appears 

 to be usual in the genus, though Jullien's figure of the genotype (Jullien 

 1888:59, plate 1, fig. 5) shows a longer ovicell without the arched 

 border. 



Canu and Bassler have described several species of this genus from 

 the American Miocene and Pliocene, but as far as I am aware the only re- 

 cent species recorded is the genotype, A. australis from Cape Horn. For 

 some thirty years I have had a small specimen from Porto Rico which is 



