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THE VOYAGE OF H.M.S. CHALLENGEK. 
Spicules. — I. Megascleres. 1. Strongyle, 0‘8 by 0'016 mm. 2. Orthotriaene, rare, 
0’48 and over by 0’016 mm., cladi 0'32 mm. long and over. 
II. Microscleres. 3. Sterraster, spherical, depressed; 010 mm. in diameter. 4. 
Oxy aster, with but few slender actines, which are sometimes not more than two in 
number, and thus indistinguishable from centrotylote microxeas ; a single actine of a 
triradiate form 0'039 mm. in length, a microxea 0'079 mm. in length. 5. Spherules, 
0‘0039 mm. in diameter. 
Colour. — Blackish-brown above where exposed to the light, whitish below. 
Habitat. — Sebenico, Adriatic ; depth, 7 fathoms. 
Genus 3. Pachymatisma, Bowerbank. 
The oscules are the single openings of cloacal chones, which lead each into a large 
cloacal cavity beneath the chonal sphincter. The incurrent chones are cribriporal. The 
somal microsclere is a microstrongyle. 
Pachymatisma j ohnstonia, Bowerbank. 
Alcyonium primum, Diosc. (?), Donati, Hist. Mer. Adriat., 1758. 
HalicJiondria joUmtonia, Bowerbank, Trans. Micr. Soc. Lond., vol. i. p. 63, pi. vi., 1841. 
„ „ Johnston, Hist. Brit. Spong., p. 198, 1842. 
Pachymatisma johnstonia, Bowerbank, Mon. Brit. Spong., vol. i. pi. xxvii. fig. 353, 1864 ; 
vol. ii. pp. 3, 51, 1866; vol. iii. p. 17, pi. viii. figs. 1-7, 1874. 
„ „ O. Schmidt, Spong. Adriat. Meeres, Suppl., ii. p. 12, 1866. 
„ „ Carter, Ann. and Mag. Nat. Hist., ser. 4, vol. iv. p. 11, 1869. 
Caminus osculosus,^ Grube, Mitth. ii. St. Malo u. Koscoff, p. 132, pi. ii. fig. 3, 1873. 
non Pachymatisma johnstonia, Hansen, Spong. Norweg. North Atlant. Exped., p. 17, pi. iv. 
fig. 15, 1885. 
Massive, raised into undulating ridges, sessile, surface smooth ; oscules and 
pores distributed over different areas, the oscules usually occupying the summits of 
the ridges. Cortex about 1 mm. in thickness, sterrastral layer thin, ectochrote well 
developed. 
Spicules. — I. Megascleres. 1. Strongyle, usually cylindrical, straight or curved, some- 
times irregularly; 063 mm. long (B.), 1‘03 by 0'013 mm. (S.), 0'924 by 0'013 mm. (R.). 
2. Orthotriaene, rhabdome conical, oxeate or strongylate, 0‘44 mm. long. (B.), 0'636 by 
0‘016 mm. (S.), 0‘44 by 0’019 (R.); cladi conical or cylindrical, oxeate or strongylate, 
013 mm. long (S.), 0'238 mm. (R.). 
II. Microscleres. 3. ellipsoidal, 012 mm. long. (B.), 0'097 byO'0838 mm. 
(S.), 0'9 by 0'07l mm. (R.). 4. Oxyaster, actines not numerous, conical, finely spined, 
^ I add here a reference to the following memoir, which I have been unable to consult ; — Koehler, E., Eemarques 
sur le genre Caminus et sur une Sponge voisine du Caminus osculosus, Grube (Paris, G. Masson, 1884). 
