REPORT ON THE TETRACTINELLIDA. 
281 
Calcahrina plicata (0. Schmidt). 
Corticium plicatum, 0. Schmidt, Spong. Algiers, p. 2, pi. iii. fig. 11, 1868. 
Sponge. — Incrusting, intergrowu with a calcareous Alga. Surface very irregular, with 
depressed conical elevations and papillm. 
Spicules. — 1. Tetractinose asters, the actines usually conical, oxeate, simple, seldom 
dichocladose ; length of an esactine 0'06 mm. 2. Microrahds, irregularly spined, 0'0083 
mm. in length. 
The microrahds are accumulated in a dense layer beneath the outer epithelium. So 
numerous are they as to render the papillae of the surface greyish- white, while the sponge 
as a whole is of a pale yellow colour. 
Habitat. — Algiers. 
Genus 3. Corticella, n. gen. 
Corticidae containing polyactinose as well as tetractinose asters. 
Corticella stelligera ,(0. Schmidt). 
Corticium stelUgerum, 0. Schmidt, Spong. Algiers, p. 25, pi. iii. fig. 6, 1868. 
Sponge. — An irregular crust, growing on Caryophylla caespitosa. Pores scattered. 
Spicules. — 1. Tetractinose aster, the three esactines are each about 0‘33 mm. in 
length, the ecactine not quite OT mm. 2. Strongylaster, actines slender, long, four to 
six in number, and one or two shorter, reduced to tubercles ; diameter, 0'05 mm. 3. Aster, 
with six to twelve short actines with wavy outline, 0'02 mm. in diameter. This spicule 
occurs in great numbers, along with the tetractinose aster (No. l), in the outer skin of 
the sponge. 
Colour. — White. Size, about 5 mm. in thickness. 
Habitat. — Sebenico and Algiers. 
Genus 4. Rhachella,^ n. gen. 
Corticidae (?) characterised by polycladose calthrops. 
Rhachella complicata (Carter). 
Samus eomplicatus, Carter, Ann. and Mag. Nat. Hist., ser. 5, vol. vi, p. 61, pi. v. fig. 27, 1880. 
Sponge. — Excavating. 
Spicule. — Microscleres. 1. Cladocalthrops, with actines repeatedly dichotomising 
actinome 0‘084 mm. in length, protocladus 0'051 mm., deuterocladus very short, trito- 
^ P»)Cos, 3- thorn-hush. 
(ZOOL. CHALL. EXP. — PART LXIII. — 1887.) 
Rrr 36 
