The Cambridge natural history . l)ut in structure ; and other evidence points the samewav. Internal Characters The interior of the shell is sometimes more or less dividctl upby septa. A median septum occuis in one; or both valves ofmany genera as a low ridge or strongly deveIo]ied partition ( Wall- 500 FOSSIL BRACHIOrODA heimia, Eig. 329, ss ; and Stringocephalus, Fig. 326, B, us). Con-cliiditim (Fig. 325) has its dental plates of great size, and unit-ing to form a Y-shaped chamber or spondylium, supported by amedian douljle septum ; and by means of these with a pair of septaand the large sock
The Cambridge natural history . l)ut in structure ; and other evidence points the samewav. Internal Characters The interior of the shell is sometimes more or less dividctl upby septa. A median septum occuis in one; or both valves ofmany genera as a low ridge or strongly deveIo]ied partition ( Wall- 500 FOSSIL BRACHIOrODA heimia, Eig. 329, ss ; and Stringocephalus, Fig. 326, B, us). Con-cliiditim (Fig. 325) has its dental plates of great size, and unit-ing to form a Y-shaped chamber or spondylium, supported by amedian douljle septum ; and by means of these with a pair of septaand the large socket-plates in the dorsal valve the interior ofthe slicll of tliis genus is divided up into several chambers. Tlie interiors of several other genera are somewhat similarhdivided up. In the Carboniferous genus Syringothyris two special plates,situated between the dental plates, are rolled into an incompletetube, so as to enclose proljaldy the anal extremity of the ali-mentary canal; and in several genera a sub-uiuli(iii;d cardiu:d. Fig. 329. — Waldheimia {MageUania)Jlavescens. A, Interior of ventral valve: a, adductorscars ; , ventral adjustors ; d, divaricators ; , accessory divaricators ; jJ, pedun-cular muscle ; dm, deltidiuin ; /, foramen ; t, teeth. B, interior of dorsal valve , anterior adductor (occlusor) scars ; , posterior adductor (occlusor) scars ;c.^j), caidinal process ; cr, crura ; , dental sockets ; hp, liinge-plato ; I, Lracliiallooii; ss, septum. (After Davidson.) plate is present, whicli is perforated (AtJtyris) or slit in somecases for the passage of the anal tube. For the support of the flesliy spiral aruis the calcareousstructures fornung the l)rachial apparatus are of two maintypes—(1) the loop type; (2) the spiral-cone type. In theStrophomenidae no special calcareous support seems to liaAe beenusually present (Fig. 334), though in some species of Leptaenaspirally-grooved elevated areas supported the fleshy arms : in theProductidae it is p
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
