EEPORT ON THE TETEACTINELLIDA. 
107 
Irregularities in the form of the calthrops are not uncommon (PI, XL figs. 15-23); 
the actines may branch, often more or less irregularly, the branches becoming crooked 
and tubercular towards their termination (PL XL figs, 17-19), and then suggesting a 
resemblance to the tetracrepid desma of the Lithistida ; in other cases the actines may be 
reduced (PL XL figs. 21-23) to three or even two in number. 
The canals of the sponge are crossed by velar diaphragms, and the aphodal canals of 
the flagellated chambers (PL XL figs. 28-31) are frequently alternately constricted and 
enlarged as though by minute vela. 
Genus 2. Calthropella, n. gen. 
Pachastrellidse with only one form of microsclere, which is a euaster. 
Calthropella simplex, n, sp. (PL X. figs. 13, 14, and 21-29). 
Sponge (PL X. figs. 13, 14). — Massive, irregularly ridge-like, with a flattened base 
and rounded sides. Surface smooth, raised in places into small rounded tubercles, each 
with a crater-like depression at the summit, from 0’15 to 0’5 mm. in diameter, and a 
centrally perforated floor, Oscules and pores similar, the central perforation of the 
tubercles leading into comparatively large, underlying cavities, from which numerous 
canals descend into the choanosome. 
Spicules. — I. Megascleres. 1. ^Calthrops of the first order (PL X. figs. 21-27) ; 
actines conical, smooth, simple, oxeate, tornote, or strongylate, 0’8 by 0'09 mm. 
The actines are frequently reduced to three in number, sometimes to one, occasionally 
they are more numerous than four; a tendency to a tubercular growth sometimes 
occurs (PL X. fig. 27). 2. Calthrops of the second order, similar to the foregoing, but 
smaller, actines 0T5 by 0‘02 mm. 
II. Microscleres. 3. Spheraster (PL X. fig. 28), centrum comparatively large ; 
actines numerous, reduced to rounded tubercles, 0'0237 mm. in diameter. A smaller 
form, 0'012 mm, in diameter, bearing fewer tubercles, is present beneath the outer 
epithelium. In the young state the actines are slender, conical, and oxeate (PL X. 
fig. 29). 
Colour. — Opaque-cream, or ochreous-white. 
Habitat. — St. lago, Porto Pray a. 
Remarks. — This sponge, which is not quite complete, measures in its present state 
90 mm. in length, it is 45 mm. broad at the base, and 38 mm. high. 
The ectosome consists of collenchyme containing numerous, deeply-stained, granule- 
cells, about O'OIG to 0’02 mm. in diameter, and elongated, fusiform cells, which are 
disposed tangentially, and render it fibrous. Its thickness is variable, in places as much 
