138 
THE VOYAGE OF H.M.S, CHALLENGEK. 
Thy one gemmata (Colochirus), Pourtalfes, 1851; Ayres, 1854; Semper, *1868. 
Thyonidium gemmatum, Selenka, 1867. Thyonella gemmata, Verrill, 
1872. (?) Thyonella sp., Eathbun, 1879. 
Deposits — oval button-like plates with undulated margins, uneven surfaces, and about 
four holes ; and reticulate cups with the often incomplete margin spinous 
or uneven. Pedicels in five distinct longitudinal series, and scattered over 
the interjacent areas. 
Habitat. — Sullivan’s Island (Pourtalfes), North Carolina (Verrill), South Carolina 
(Ayres, Selenka), Fort Macon (Coues and Yarrow), Florida Eeef (Pourtales) 
(?) Bahia (Eathbun). 
According to Ayres, the radial pieces of the calcareous ring are prolonged posteriorly 
into two slender branches. Judging from the figure given by Selenka, they are 
only slightly excavated posteriorly. 
II. Calcareous ring of ten simple pieces, the radial with a bifurcate 
prolongation posteriorly. 
Thy one ovulum [Stolus), Selenka, 1867 ; Semper, 1868. 
Excepting terminal plates in the pedicels, no deposits. Pedieels very numerous. 
Habitat — Acapulco (Selenka). 
Thy one mirabilis, Ludwig, 1875. 
Deposits — scattered tables, composed of a roundish perforated disk and a spire of two 
anastomosing rods. Body slightly quadrangular, with a row of small warts along 
the dorsal ambulacra. Ventral pedicels much more numerous than the dorsal. 
Habitat . — Bowen (Ludwig), Port Denison (BeU). 
III. Calcareous ring of ten pieces, each composed of a great number of small 
parts ; posteriorly it carries five bifurcate prolongations. 
Thy one sacella [Stolus), Selenka, 1867 ; Semper, 1868 ; von Marenzeller, 1881. Thy one 
rigida. Semper, 1868. 
Deposits — Numerous, somewhat irregularly formed bodies, consisting of a plate with 
four holes and a smaller bow vertically disposed on each side, thus presenting the 
view of two rings placed vertically to one another ; the larger plate or ring has 
the undulating rim provided with low elevations. 
Hahitat . — Bohol (Semper), Japan (von Marenzeller), Torres Strait (Bell), Aden 
(Semper), Zanzibar (Selenka), Mozambique (Semper). 
