. Carnegie Institution of Washington publication. 146 Papers from the Marine Biological Laboratory at Tortugas. chinus when oculars begin to enter the periproct, the first to enter is V or I, but in the Montego Bay series V is by far the more common/ they being in the ratio of 102 of ocular V to 23 of ocular I. In this feature Centrechinus makes an approach to the Cidaridae, in which group, when one ocular is insert, it is almost always ocular V. As previously shown, when in the Centrechinoida four oculars reach the periproct, it is typically I, V, IV, II, and when any other combination exists
. Carnegie Institution of Washington publication. 146 Papers from the Marine Biological Laboratory at Tortugas. chinus when oculars begin to enter the periproct, the first to enter is V or I, but in the Montego Bay series V is by far the more common/ they being in the ratio of 102 of ocular V to 23 of ocular I. In this feature Centrechinus makes an approach to the Cidaridae, in which group, when one ocular is insert, it is almost always ocular V. As previously shown, when in the Centrechinoida four oculars reach the periproct, it is typically I, V, IV, II, and when any other combination exists it is nearly always I, V, IV, III. This combination, while rare in the Centrechinoida as a whole, is rela- tively more frequent in Centrechinus and is a typical feature or a frequent variant in some species of the Cidaridae. In this feature also, therefore, Centrechinus makes a certain approach to the Cidaroida. In Centrechinus, when opened fresh and alive, it is found that the teeth extend above the base of the foramen magnum about to the upper line of the lantern, but the proximal base of the teeth does not extend horizontally over the lantern as in the Echinidse, Strongylocentrotidae, and Echinome- trldse. Further, the dental capsule, inclosing the base of the tooth, is small. In the limits of the teeth dorsally and the small dental capsule, as well as in the grooved teeth, Centrechinus makes a close approach to the characters of the Cidaridae as represented by Eucidaris trihuloides. M 3 Figs. 2-6.—Perignathic girdle in Aspidodiadema and its development in Centrechinus. 2.—Adult Aspidodiadema meijerei (Doderlein), Pailolo channel, Hawaiian Islands. The auricles are separate spur-like styles. 3.—Centrechinus setosus (Leske), Montego Bay, Jamaica. Specimen 5 mm. diameter. Auricles are separate styles, apophyses faint. 4-—The same. Specimen 10 mm. diameter. Auricles are more developed and arch over the ambulacra. S.—The same. Specimen 25 mm. diameter. Auricles meet o
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