A treatise on zoology . Amb Fig. XLV. Protocrinus oviformis, after Volborth. 1, oral surface, showing food-grooves partly coveredby ambulacrals, x 3; 2, aboral surface of young individual, showing stem-attachment; 3,aboral surface of oldindividual, without portions of adambulacrals. Each adambulacral bears a brachiole-facet;there are about thirty-six in each ray. Family 4. Mesocystidae. Diploporita in wliich the food-groovesextend over the theca almost to the aboral pole, and are regularlybordered by alternating brachioliferous adambulacrals, raised above andoutside the adjacent interam
A treatise on zoology . Amb Fig. XLV. Protocrinus oviformis, after Volborth. 1, oral surface, showing food-grooves partly coveredby ambulacrals, x 3; 2, aboral surface of young individual, showing stem-attachment; 3,aboral surface of oldindividual, without portions of adambulacrals. Each adambulacral bears a brachiole-facet;there are about thirty-six in each ray. Family 4. Mesocystidae. Diploporita in wliich the food-groovesextend over the theca almost to the aboral pole, and are regularlybordered by alternating brachioliferous adambulacrals, raised above andoutside the adjacent interambulacrals. Diplopores confined to inter-ambulacrals. Five interradial deltoids (A) sur-round the peristome. In this family we reachthe final stage of the Diploporita, although abranch parallel with the Mesocystidae passes onin the direction of the Eublastoidea, beyond theboundary of the Cystidea. Genera—Mesocystis,Bather (Jan. 1898, =Mesites, Hoffmann, 1866;Nikitin, 1877 ; Agelacrinus, Schmidt, 1874),Ordovician, Esthonia. Theca (Fig. XLVII. 1)simulates that of a regular echinoid, or still more, ^^^^Eclrioaster, since the mouth is on the uppersurface; from it narrow food-grooves, protectedby covering-plates, pass straight down to the ^^^- ^^^i- margin of
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