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PACIFIC SCIENCE, VoL XIX, April 1965 
Schmidt and Myriastra Sollas on the grounds 
that species of Myriastra possess only one type 
of aster, a chiaster or tylaster, was admittedly 
arbitrary; the opposite view has been taken by 
Burton (1926). It is not consistent to limit 
stellettid genera by the possession of a single 
and widespread type of aster. Species such as 
Myriastra debilis Thiele have only oxyasters. 
Such a sponge is not, in Dendy’s view, a Myri- 
astra. If the generic diagnosis is to be widened 
to admit it, then the argument that a genus can 
be limited by the possession of a single micro- 
sclere category when a closely related genus ex- 
hibits a variety of microscleres, including this 
type, obviously cannot be upheld. It would lead 
to the establishment of individual genera for 
every stellettid with only one type of micro- 
sclere. Both tylasters and oxyasters are common 
among species which have been referred to 
Stelletta and it is preferred here, following 
Burton, to regard all species possessing only a 
single microsclere category as belonging to this 
genus. 
FAMILY TETILLIDAE Sollas 
GENUS Tetilla Schmidt 
Tetilla microxea n. sp. 
Fig. 33 a, b 
OCCURRENCE: Sta. 53 (one specimen, the 
Holotype, USNM 23700). 
DESCRIPTION: A small, hemispherical sponge 
growing upon a coral fragment; unfortunately 
Fig. 33<z. Tetilla microxea n. sp. Sta. 53. Holotype. 
USNM 23700. 
the specimen is damaged and approximately 
half remains attached. The characteristic fea- 
ture of the specimen is the presence of long 
projecting surface spines each made up of one 
to twelve stout oxeas. 
The sponge is 1.9 cm high, 1.6 cm wide, and 
the surface spines range from 2.5 to 7.0 mm. 
Basal rooting tufts, frequently well-developed In 
species of Tetilla , are only just indicated at the 
base of this specimen. 
COLOR: In alcohol, reddish-brown (YR 5/4) 
externally, pale brown internally (approxi- 
mately yY-R 7/4). 
TEXTURE: Firm, compressible. 
SURFACE: Conulose, spiny, and granular. 
Each projecting radial tract raises the skin-like 
ectosome into a marked conule and the tissue 
surrounding the spicules may extend up to 2.5 
mm beyond the level of the sponge surface. 
Conules are spaced relatively regularly over the 
surface, approximately 1-3 mm apart. The ac- 
tual surface tissue of the sponge appears gran- 
ular, contains abundant sigmas and microxeas, 
and has a considerable amount of detritus and 
large foraminiferans adhering to it. No pores 
or oscules are apparent. 
SKELETON: Tracts of large oxeas radiate 
from the center of the sponge to the surface; 
occasional megascleres occur between these 
tracts but the predominant spicules in this posi- 
tion are microxeas. Both protriaenes and ana- 
triaenes are present in addition to the oxeas 
in the endosomal skeleton; these spicules are, 
however, extremely rare. There is no layer of 
radially disposed cortical oxeas and no special 
disposition of the triaenes. The sigmaspirae are 
extremely abundant in the dermal region and 
in the outer half of the endosome; microxeas 
have a similar distribution. 
SPICULES: Megascleres. (a) Oxeas, large 
straight spicules frequently stair-stepped, taper- 
ing to sharp points, (b) Anatrlaenes, with flat- 
tened cladome, very slightly recurved rays and 
long lash-like rhabdome. These spicules are rare 
overall but seem to occur in groups associated 
with the endosomal oxeas, not, as in many 
tetillids, concentrated toward the base of the 
sponge, (c) Protriaenes. Only two spicules 
were found, one with stout straight shaft and 
irregular cladi, the other a fine prodiaene, with 
