DENDY—REPORT ON THE CALCAREOUS SPONGES 11 
membrane the spicules lie tangentially, and a few very large triradiates are scattered here 
and there amongst the small ones. 
The spicules (Plate 4, fig. 2) are equiangular and approximately equiradiate tri- 
radiates, of three kinds:—(1) Small, with straight, conical, gradually sharp-pointed 
rays measuring about 0°19 by 0°0174 mm. (at base). These form the whole of the 
skeleton of the choanosome and the greater part of the dermal skeleton. (2) Large, 
with straight, conical, gradually sharp-pointed rays measuring about 0°59 by 0°046 mm. 
(at base). These occur sparsely scattered in the dermal membrane only. (3) Small, 
resembling (1) but rather smaller, and with two of the rays bent sharply back near their 
bases until they come to extend nearly at right angles to the third ray. These occur 
in the oscular margins, along or parallel to which their bent rays are extended. 
As regards histology the condition of the specimens allows me to say very little, but 
it is worth observing that the nuclei of the collared cells are distinctly basal. 
This species is evidently nearly related to Leucetta microraphis Haeckel, but my 
specimens of that species (from Port Phillip, Australia) have the large triradiates much 
larger (and especially stouter) and scattered all through the sponge instead of being 
confined to the dermal surface. 
The specimens of L. chagosensis all came from the Chagos archipelago. 
Register Nos., Localities, dc. uxtit., Lagoon, Diego-Garcia, 8.7.05 ; cx. 10, Egmont 
Reef; oxi. 5, Egmont Lagoon; cx1x. 11, Salomon. 
5. Leucetta pyriformis n. sp. 
(Plate 1, fig. 7; Plate 4, fig. 3.) 
This pretty little species was represented in the collection by two specimens which 
closely resembled one another in external form, each being a single, small, pear-shaped 
individual with a single terminal vent at the broad end. 
Specimen xc. 5, A, which may be taken as the type, is represented in Plate 1, fig. 7. 
It measured about 10 mm. in height by 5°5 mm. in greatest breadth. The texture was 
harsh owing to the presence of the very large triradiate spicules, which could be clearly 
seen on the surface with a lens, as shown in the photograph. The colour in spirit was 
hight brown, but this may have been due to accidental staining by other specimens in the 
same jar. 
The canal system is typically leuconoid.. Wide inhalant canals commence beneath 
the thin, pore-bearing dermal membrane and run inwards at right angles to the surface, 
interdigitating with exhalant canals which open into the central gastral cavity. Both 
Systems are of course more or less branched, and between them lie the rather large 
flagellate chambers, closely packed together and without order. The chambers are 
oval or nearly spherical, often polygonal from mutual pressure ; they are eurypylous and 
have numerous prosopyles; they measure about 0-174 mm. in maximum diameter. 
The dermal skeleton consists of several confused layers of large and small triradiates 
placed tangentially. The skeleton of the chamber layer also consists of large and small 
triradiates, thickly and irregularly scattered. There is a well-developed, though not very 
9) 
Aa—a4 
