A MONOGRAPH OF THE EXISTING CRINOIDS 219 



AcHnometra iowensis Springer, American Geologist, vol. 30, 1902, p. 98 (preliminary description). — 

 Bull. Lab. Nat. Hist., Univ. Iowa, vol. 5, No. 3, 1903, p. 217 (detailed description; comparisons; 

 side and covering plates); pi. 1, figs. 1-6. — Minckert, Archiv f. Naturgesch., Jahrg. 71, 1906, 

 vol. 1, Heft 1, p. 176, footnote; p. 207 (syzygies; regeneration). — Hamann, Bronns Klassen 

 und Ordnugen des Tier-Reichs, vol. 2, Abt. 3, 1907, p. 1586 (listed). 



Comasler iowensis A. H. Clark, Proc. U. S. Nat. Mus., vol. 33, 1908, p. 686 (listed); vol. 35, 1908, 

 pp. 120, 123 (arm structure); p. 124 (listed); vol. 36, 1909, p. 362 (ambulacral plating). 



Nemaster iowensis A. H. Clark, Vidensk. Medd. fra den naturhist. Forening i K0benhavn, 1909, 

 p. 118 (history of the discovery); Ann. and Mag. Nat. Hist., ser. 8, vol. 5, 1910, p. 361 (side 

 and covering plates). — H. L. Clark, Bull. Lab. Nat. Hist., Univ. Iowa, vol. 7, No. 5, 1918, 

 p. 7 (history). — A. H. Clark, Univ. Iowa, Studies in Nat. Hist., vol. 9, No. 5, 1921, p. 7 

 (Bahamas; Tortugas; Dominica; littoral); p. 8 (obtained by the Barbados-Antigua expe- 

 dition); p. 22 (stations 53, 97, 98, 99, 100; Engineers' Pier, Barbados; Barbados); pp. 27, 

 28 (listed); Smiths. Miscell. Coll., vol. 72, No. 7, 1921, pi. 16 (photograph of a specimen from 

 the Bahamas). — H. L. Clark, Littoral Echinoderms of the West Indies, 1921, p. 53 (Tortugas; 

 Bermuda [in reality Bahamas]). — A. H. Clark, The Danish Ingolf-E-xped., vol. 4, No. 5, 

 Crinoidea, 1923, p. 38 (range). 



AcHnometra echinoplera var. {'>)lineata Hartlaub, Mem. Mus. Comp. Zool., vol. 27, No. 4, 1912, 

 p. 471 (quotation of Carpenter's remarks). 



AcHnometra echinoplera var. discoidea (part) Hartlaub, Mem. Mus. Comp. Zool., vol. 27, No. 4, 

 1912, p. 464, pi. 17, fig. 14 ("apparently" Montserrat, 88 fathoms). 



AcHnometra blakei (not of P. H. Carpenter, MS.) Hartlaub, Mem. Mus. Comp. Zool., vol. 27, 

 No. 4, 1912, p. 471 (Blake station 171; the specimen described, but not the one referred to); 

 pi. 13, fig. 9. — Hamann, Bronns IClassen u. Ordnungen des Tier-Reichs, vol. 2, Abt. 3, 1907, 

 p. 1584 (listed). 



AcHnometra echinoptera var. miilHcirra Hartlaub, Mem. Mus. Comp. Zool., vol. 27, No. 4, 1912, 

 p. 472 (Blake station 171; description [under the name blakei]); pi. 13, fig. 9. 



Diagnostic features. — This species resembles A'', grandis very closely, but the 

 cirri are much shorter, from 10 to 14 mna. in length, with only 12-18 segments; 

 the arms are 23-43 in number, from 90 to 135 mm. long. The color in life varies 

 from sulphur yellow to golden brown or black, imiform or in the dark individuals 

 with yellow tips to the pinmdes. In alcohol most of the specimens are uniform 

 dark olive green. 



The absence of a dark mediodorsal stripe on the arms distinguishes it from 

 A'^. ruhiginosa, and the absence of a dark spot on each pinnule segment distinguishes 

 it from A^. discoidea. It is also larger and stouter than either of these, with stouter 

 cirri. 



Description. — The centrodorsal is thin discoidal, with the dorsal pole broad and 

 very slightly concave, 6 mm. in diameter. The cutus sockets are arranged in 2 

 alternating and more or less confluent marginal rows. 



The cirri are XXX, 14-18 (in most cases 16), very strongly and evenly recurved 

 and about 25 mm. long. The first segment is very short, the second is almost twice 

 as broad as long, the third is from slightly longer than broad to half again as long 

 as broad, and those following gradually increase in length to the seventh or eighth, 

 which is from half again to almost twice as long as the narrowest width (at the end 

 of about the basal third); from this point onward the segments gradually decrease 

 in length distally. so that the last 3 are usually broader than long, sometimes about 

 as long as broad. The ventral profile of the segments is slightly concave, but the 

 dorsal nearly straight; the ends are somewhat swollen and projecting, especially 



