REVISION OF FRESHWATER SPONGES OF SPONGILLIDAE 153 



Microscleres not yet recorded. 



Gemmoscleres of two different tj'pes and series: an inner layer of 

 typically tubelliform scleres wdth a delicate smooth shaft, their lower 

 rotule well developed, circular, and sUghtly curved inward, their 

 upper rotule represented by a knoblike structure; and an outer layer 

 of short and thick birotulates of unequal length, consisting of a 

 straight smooth shaft and terminally of umbonate heads of equal 

 size, their circular margins regularly divided into a small number of 

 strongly recurved and stout conical teeth. 



Gemmules moderately large and spherical; pneumatic layer well 

 developed and granular; gemmoscleres embedded in this layer radially 

 in two series: (1) Tubelliform spicules resting with their large rotule 

 on the inner gemmular membrane, and reaching with their knobs 

 to outer membrane; (2) birotulates with thek lower rotule embedded 

 in outer gemmular membrane, with their upper projecting beyond 

 it; foramen tubular, porus tube short and straight. 



Sponges forming thin film on sohd support; siu-face recorded as 

 even; color in life not yet observed; consistency fragile, crumbHng. 



Known only from South America. 



Discussion. — The rejection of the entire system of Gray (1867) by 

 Carter (1881a) caused the sufficiently defined but forgotten genus 

 Acalle to remain in obsciu-ity for almost 70 years. Burton (1934) 

 was first to reintroduce this genus in spongillid taxonomy but errone- 

 ously appHed it to a Metania species, namely Tubella pottsi Weltner. 

 In a later paper. Burton (1938) fisted Acalle as a synonym of Metania, 

 correctly referring to Spongilla reticulata as the type species of the 

 latter genus. Thus for the second time Acalle fell into obscurity 

 until JeweU (1952) reestabfished it, naming Spongilla recurvata 

 Bowerbank as its type species by monotypy. 



De Laubenfels (1936) loosely compared Acalle with Asteromeyenia, 

 now a synonym of Dosilia, and drew attention to the fact that both 

 possess "two types of microscleres." However, this criterion cannot 

 be used for an assessment of an intergeneric relationship since the 

 two series in Acalle are gemmoscleres, whereas in Asteromeyenia they 

 are free microscleres. 



Acalle is most closely related to Metania, from which it differs 

 chiefiy in the possession of an outer series of birotulates resembfing 

 those of Heteromeyenia species, and in the absence of free micro- 

 scleres. The chance that the outer birotulates could be adventitious 

 is unfikely though not impossible. Only future studies of the only 

 representative of Acalle, apparently found on only two occasions, 

 will decide whether the genus can be retained or whether it finally 

 should be relegated to a synonym of Metania. 



