A treatise on zoology . )n)xiniale (Fig. LII.).Continuance of this process led to the evolution, along manydinerent lines, of crinoids that are generally described as un-stalked, and for which older writers were wont to erect an order,Astylida. These fall into three groups: First, those in which aportion of the stem remains, becoming compressed and fused, with orwithout the infrabasals, into a cirrus-))euring compound ossicle, to. Fin. LI. Grapnel of Miirtillncrums (afterHall). Millericrinus Pratti all THE CRINOIDEA J35 which the term centro-dorsal was originally applied, and to whichit must b
A treatise on zoology . )n)xiniale (Fig. LII.).Continuance of this process led to the evolution, along manydinerent lines, of crinoids that are generally described as un-stalked, and for which older writers were wont to erect an order,Astylida. These fall into three groups: First, those in which aportion of the stem remains, becoming compressed and fused, with orwithout the infrabasals, into a cirrus-))euring compound ossicle, to. Fin. LI. Grapnel of Miirtillncrums (afterHall). Millericrinus Pratti all THE CRINOIDEA J35 which the term centro-dorsal was originally applied, and to whichit must be restricted { Antedon, Eudiocrinus, Thaumatocrinus ; seeFigs. ). These forms anchor themselves by theircirri, and though capable of ci-awling, climbing, and swimming, donot often exercise their faculty of locomotion. Secondly, the groupin which either a portion of remaining stem, or the lower part ofthe cup { BB or IBB), l)ecomcs solidified, usually by additionaldeposition of stereom, into a knob, which, one may suppose, servesas ballast or as a sea-anchor ; such forms are Agasskocrinus (p. 181),Edriocrimis (Pig. CXIL), and Millericrinus Fratti (Fig. LIT.). Bothof these groups have a small calycal cavity with thick walls, andthere can be little doul)t but that all are attached by a stem in theearlier stages of ontogeny. The third group, comprising Marsupites(Fig. CIV.), Saccocoma (Fig. LXVIIL), and Uin
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