Cxviii THE VOYAGE OP H.M.S, CHALLENGER. 
In an article in tlie Encyclopaedia Britannica I proposed the following classification, 
which is based on differences in the characters of the desmas : — 
Order Lithistida, 0. Schmidt. 
Suborder I. Tetracladina (Zittel). The desma is tetracrepid. 
Family I. Tetracladidse. With the characters of the suborder. Examples — Theonella, 
Gray ; Discodermia, Bocage ; Siphonia, Parkinson. 
Suborder II. Ehabdocrepida. The desmas are of various forms, founded on a mono- 
crepid basis. 
Family I. Megamorinidse (Zittel, emend.). The desmas are of comparatively large size ; 
the ectosomal spicules are trisenes and the microscleres are usually spirasters. Examples 
— Corallistes, 0. Sch.; Dorydermia, Zittel; Hyalotragos, Zittel; Lyidium, 0. Sch. 
Family II. Micromorinidse. The desmas are of comparatively small size, trisenes 
and microscleres are absent. Examples — Azorica, Carter ; Verruclina, Zittel. 
Suborder HI. Anomocladina. The desmas with a nucleate massive centrum from 
which a variable number of arms proceed radiately. Examples — Vetulina, 0. S.; Astylo- 
spongia, Koemer. 
On becoming convinced of the occurrence of the passage from the tetracrepid to the 
monocrepid desma, discovered by 0. Schmidt to occur in the case of Macandrewia ; and 
further recognising the closeness of the affinity which exists between the Tetracladidse, 
and Megamorinidse (as defined above), I made a fresh attempt at classification, and this 
time based it on the presence and absence of trisene spicules ; thus making primary use 
of the same character that is employed for the separation of the Choristida from the 
Monaxonida. 
In this way the order Lithistida would be divided into two suborders, the Trisenophora 
and Ehabdophora. The Trisenophora would be distinguished not only by trisenes but 
by the presence of microscleres and by the larger size of the desma. 
Further investigation, however, revealed the presence of microscleres in two 
Ehabdophorous genera (Scleritoderma and Neopelta) ; in the latter an amphiaster is 
present, in the former a sigmaspire, precisely similar to the typical sigmaspire of the 
Tetillidse. 
These genera thus agree with the Trisenophora in possessing microscleres, and with 
the Ehabdophora in the absence of trisenes. They are truly annectant, or passage-forms 
through which the Trisenophora pass into the Ehabdophora. If they are to be classed 
with either group it should be with the former since they further resemble them in 
possessing a special ectosomal spicule. Their inclusion however necessitates a change 
in the proposed classification, and I now offer the following, in which the presence or 
absence of special ectosomal spicules and of microscleres serves for the definition of two 
suborders — the Hoplophora and Anoplia ; the Hoplophora are subdivided into two demi. 
