no. 1G3G. ARM HOMOLOGIES IN RECENT CRINOIDS— CLARK. 



117 



Fig. 8. — D o u s a i. view 



OF AN AXILLARY, ALL 

 THREE OP WHOSE FACES 

 ARE "OBLIQUE MUSCU- 

 LAR ; " THE ARTICULA- 

 TION BETWEEN THE TWO 

 TOST-AXILLARY .HUNTS 

 IS ALSO " OBLIQUE MUS- 

 CULAR." 



joint by a straight muscular, and to the succeeding by an oblique 



muscular articulation. Having now discovered a 



pair of joints, which we may for convenience 



call Zj and Z 2 , which are, no matter where they 



may be, always readily identifiable, we are now 



ready to enter into a detailed discussion of the 



brachial homologies. 



Note. — In the illustra- 

 tions Z x is in all cases dot- 

 ted, and Z 2 is solid black. 

 Pentametrocrinidce (figs. 

 9, 10, 12, and 13).— I re- 

 cently" separated under the 



name of Pentametrocrinus (figs. 9 and 10) the 

 species allanticus, japonicus, semperi, tubercu- 

 latus, and varians, which had previously been 

 confused, because of their undivided arms, 

 under the generic name of Eudiocmnus, with 

 Eudiocrinus indivisus and granulatus, on ac- 

 crinus (adapted from coimt f fl^ simplicity of their arm structure, 



P. H. Carpenter.) . , J 



which agrees with that ot the species Decame- 



trocrinus (fig. 13) and with Thaumatocrinus 



(fig. 12) which also have undivided arms, with 



which I united them under the family name of 



Pentametrocrinidse. 



In this family, Pentametrocrinidse, we find 

 the following sequence 

 of articulations : straight 

 muscular between the ra- 

 dials and the following 

 joints; synarthrial be- 

 tween the first and sec- 

 ond post-radial joints; 

 oblique muscular between 

 the second and third 



Fig. 9. — Pentametko- 

 crinid.e ;Pentametro- 



Fig. 10. — Proximal paetof 

 arm (if Pentametrocri- 

 nus t uberc u la t r s , 

 showing the external 

 appearance of the ar- 

 ticulations. 



post-radial joints; we at 



Fig. 11. — Proximal tartof i J 



arms of thaumatome- once recognize, therefore, the joints Z t and Z 2 , 

 » SSSiTS: f '"' all the succeeding articulations, as isalways 



ante of thearticula- the ease after the first oblique muscular articu- 

 lation, are also dblique muscular, or more 

 rarely, syzygies. Thus the family Pentametrocrinidse exhibits the 



Now Genera of Unstalked Criuoids, Proc. Biol. Soc. Washington, XXI, pp. 

 125-136 (April 11, 190S). 



