A treatise on zoology . djoining eating with the thecal cavitv. Trochovystis text. o ^ . „ may be regarded as a differentiation fromsuch a form as Aristocystis by lateral compression^ so that its broadmedian plane is morphologically thesagittal, and the flat sides are theprimitive right and left, the pro-jecting i)late M being on the left , Barrande (1887), Cam-brian and Ordovician (Fig. XII.),has twelve marginals {mm), but onthe (left ?) side that corresponds withthe convex side of later forms, thejunction of the stem with the somaticplates lies between two of them ;wliili^ th
A treatise on zoology . djoining eating with the thecal cavitv. Trochovystis text. o ^ . „ may be regarded as a differentiation fromsuch a form as Aristocystis by lateral compression^ so that its broadmedian plane is morphologically thesagittal, and the flat sides are theprimitive right and left, the pro-jecting i)late M being on the left , Barrande (1887), Cam-brian and Ordovician (Fig. XII.),has twelve marginals {mm), but onthe (left ?) side that corresponds withthe convex side of later forms, thejunction of the stem with the somaticplates lies between two of them ;wliili^ the median adoral plate ofthis side (M) is vertically grooved onthe interior, but exteriorly resembh-sthe somatic phites, which on tliisside, tliough hirger and fewer (50-60)tlian in Tnu-horydia, still form amoMuic of liexagona ; two, adjoiningthe stem, arc larger than the the other side, which corresponds witli the concave side of later forms, Fig. XI. Trochocystis bohemicus, restored on the evidence of Bar. Fio. -Ml. viitm. I, Imm supixKsod riglitside ; J, frimi siinposfd lolt sitlo ; It, intfriori>f uppfT put 11)1 tlio liitler, showing the loldinlphit<i M. (AftiT ltarrnn<l<<.) THE CYSTJDEA \ .SI \\w inarginals have extended far over the area formerly occupied by somaticl)laUs, ami these hitter number from three to six, one of whicli is much thelargest and of irregular shape. Openings other than the median not of about four alternating rows of plates, often provided with thorn-likeprocesses, and each overlapping its distal neighbour ; total length aboutequal to that of the theca, the proximal third with a wide lumen. Noother appendages observed. Atelecystis {A. Huxleyi), Billings (1858), isimperfectly known ; Anomalocystis cornutuSj Hall (1859), may be con-generic, as usually supposed ; but A. disparilu^ Hall, probably belongs toPlacocydis {vide infra). All the species described by P^arrande (1887) asAnomnlocystis are doubt
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Keywords: ., bookcentury1900, bookdecade1900, bookpublishe, booksubjectzoology
