134 U-S. NATIONAL MUSEUM BULLETIN 2 72 



Gemmules often very abundant, extremely small and subspherical 

 to spherical; pneumatic coat well developed but usually very thin, 

 consisting of small rounded air spaces; both gemmular membranes 

 well developed; gemmoscleres embedded in the pneumatic coat 

 radially, usually forming one layer only, their inner rotules often 

 overlapping each other; gemmules sometimes encased in a capsule of 

 normal megascleres; foramen simple to slightly tubular, always some- 

 what elevated. 



Sponges forming shallow but often extensive encrustations on 

 various substrata; surface hispid and uneven, with a number of short 

 and erect tubular projections; most species apparently shunning Ught. 

 Coloration a dark brown. Consistency moderately soft to very hard. 



Widely distributed throughout the world as a genus, though most 

 species possess more or less sharply defined zoogeographical boundaries. 



Discussion. — The genus Trochospongilla was among the first newly 

 erected genera designed for a clearer subdivision of the Meyeninae 

 Carter, considered by most previous authors as a separable subfamily. 

 At the time of its erection, only four of the six then known species 

 seemed to fit the generic definition by Vejdovsky (1883b), and the 

 two remaining obvious congeners T. paulula and T. pennsylvanica 

 were retained in the superficially apphcable genus Tubella Carter by 

 even some most recent authors. Although the gemmosclere rotules of 

 some Trochospongilla species are equal in size and shape, the upper 

 rotule of the majority of species is invariably smaller, and it is not 

 surprising to find some extremes in which the upper rotule is very small, 

 or even rudimentary. All the species of Trochospongilla, as here re- 

 defined, form a distinct group of spongillids and none of them can be 

 considered to belong to another genus. Annandale (1911c), while 

 describing additional species from Asia, was first to demonstrate the 

 proper generic position of T. pennsylvanica, and Gee (1926-1932) 

 correctly used the generic name of Trochospongilla also for T. paulula, 

 the type species of Tubella Carter, now a synonym of Metania Gray. 



Some nomenclatural problems will still have to be solved in the 

 clearly distinct genera Trochospongilla and Metania, as here redefined. 

 The genus Uruguay a, designed by Carter (1881a) for the inclusion of 

 only one species with the gemmules still unknown, now contains a 

 number of closely related species displaying features of great similarity 

 to those of Trochospongilla. Annandale (1911c) suggested the relega- 

 tion of Uruguaya to a subgenus of Trochospongilla, a taxonomic pro- 

 cedure which would be impossible to follow, since the first genus has a 

 priority of two years over the second. At present these two genera are 

 still separable by their greatly differing structure of their skeletons, 

 which in Uruguaya is of almost stony consistency, as well as by a num- 

 ber of minor criteria. However, future research may demonstrate 



