Page:Lipsanocystis traversensis, a New Cystid from the Devonian of Michigan.pdf/4

156 Plates 10, 11, 12, 13, 14, (15), in third row;

Plates 16, 17, 18, (13), 19, 15, in fourth row;

Deltoid 23 double, in fifth row.

Deltoid 23 is double, and contains both the madreporite and the hydropore. The former is divided, and appears as two elevations, each with an orifice in its apes. The hydropore appears as a small circular opening below and between the two parts of the divided madreporite.

Anal opening moderately large, entirely enclosed by plate 13, except for about 2 mm of its periphery, which is formed by the upper edge of plate 8. One basal and 2 upper pectinirhombs, with numerous dichopores, situated respectively on plates 1 and 3, 14 and 15, and 12 and 18. The halves of the pectinirhombs on plates 5, 14, and 12 surrounded by conspicuous raised margins, those on 1, 15, and 18 without mariginal walls.

Ambulacra four, simple, extending to the basal row of plates. These are RI, RII, RIV, and RV. Brachioles relatively few in number and rather widely separated.

Column unknown.

Genotype, L. traversensis. No other species known.

Lipsanocystis shows in its structure relationship with other Apiocystinae, especially Apiocystites and Tetracystis. Dr Charles Schubert, who has examined the specimen, pronounces it "a changed Apiocystites, having become more depressed and therefore has changed somewhat the arrangement of the plates." It has pectinirhombs resembling somewhat those of Tetracystis chrysalis Schuchert, but differs from all other genera of the family in having the anal opening almost entirely enclosed by plate 13, only a small part of the border being formed by plate 8. (See Text Fig. 5.) Since this genus is apparently a holdover of a Silurian type, the name Lipsanocystis is given to it.