PART 5 A MONOGRAPH OF THE EXISTING CRINOIDS 777 



prctation of stnicturo; young of Promachocriniis abyssorum) ; Crinoids of the Indian Ocean, 1912, 

 p. 32 ( = Pentametrocrinus, sp.), p. 250 (included in Penlamelrocrinus) , p. 251; Smithsonian Misc. 

 Coll., vol. 61, No. 15, 1913, p. 67 (published references to specimens in the B.M.; Challenger stas. 

 147, 158; notes); Journ. Washington Acad. Sci., vol. 5, No. 3, 1915, p. 81 (Antarctic; range); 

 Die Crinolden der Antarktis, 1915, p. 104 (collected by the Gauss), p. 106 (collected by the 

 Challenger; recorded as Thaumatocrinus renovatus-\- Protnachocrinus abyssorum), p. 107 (in key to 

 antarctic crinoids), p. 149 (in key to the species of Thaumatocrinus), p. 150 (synonymy; Gauis 

 records; previous records), p. 170 (a deep water antarctic species; range), p. 171 (systematic and 

 geographical relationships), p. 193 (further discussion), pi. 9, figs. 1, 2; Unstalked crinoids of the 

 Si'fcoso-E.xped., 1918, p. 259 (in key; range). — Bather, Ann. Mag. Nat. Hist., ser. 9, vol. 1, No. 4, 

 1918, p. 299 (interradi-als).— A. II. Clark, The Danish Ingolf-'ExpcA., vol. 4, No. .5, 

 Crinoidea, 1923, p. 17 (compared with T. jungerseni). — Gisl^n, Zool. Bidrag Uppsala, vol. 

 9, 1924, p. 20 (position of lowest pinnule); Ark. Zool., vol. 19, No. 32, 1928, p. 12 (notes); Rep. 

 Swedish Deep Sea Expcd., vol. 2, Zool., No. 4, 1951, p. 56 (depth range). 



Taumalhocrinus renovalus Perrier, Traite de zoologie, 1893, p. 858. 



Decamelrocrinus abyssorum Minckert, Zool. Anz., vol. 28, No. 13, 1905, p. 501. — A. H. Clark, Proc. 

 U.S. Nat. Mus., vol. 34, 1908, p. 216 (compared with rugosus); Mem. Australian Mus., vol. 4, 

 1911, p. 796 (locality); Journ. Washington Acad. Sci., vol. 2, No. 13, 1912, pp. 312-314 (adult of 

 T. renovalus; growth of the latter) ; Crinoids of the Indian Ocean, 1912, p. 33 {— ProTnachocrinus 

 abyssorum P. H. Carpenter, 1888), p. 248 (synonymy; localities). 



Penlamelrocrinus, sp. A. II. Clark, Mem. Australian Mus., vol. 4, 1911, p. 796; Crinoids of the Indian 

 Ocean, 1912, p. 32. 



Promachrocrinus abyssorum Koehler, Les 6chinodermes des mers d'Europe, vol. 1, 1924, p. 58 (depth) . 



Thaumalrocrinus renovalus Koehler, Les ^chinodermes des mers d'Europe, vol. 1, 1924, p. 58 (depth). 



Diagnostic Jeatures. — None of the si.\ known specimens exceeds a size of 3.5 mm. 

 diameter of centrodorsal and 4 mm. length of the first 4 brachials; the ccntrodorsal is 

 low conical wath a distinct ape.x and bears up to XX cu-ri, of which the basal 2 or 3 seg- 

 ments are short but the rest are probably several tinics longer than broad; the pro.ximal 

 pinnules are long, with ov^er 15 segments, those of Pi being not more than twice as long as 

 broad; the segments of the distal pmnules are progressively more elongated. 



Description [by A.M.C.]. — The specimen from Challenger station 158, which is one 

 of the syntypes of Promachocrinus abyssorum Carpenter, has the centrodorsal low conical 

 vdth the dorsal pole coming to a distinct peak. It is 3 mm. in basal diameter and 

 1.2 mm. high. There are XIV cutus sockets of which the rims are ver^^ prominent 

 except at the distal end. Three segments of the base of one cirrus remain attached. 

 They are all short; even the third is shorter than broad. 



The first four brachials together measure 4 nmi. in length. The width at tlie first 

 sj'zygy at 4 + 5 is 1.3 mm. The second s3'Z3^gy is usually at 9 + 10. The distal inter- 

 syzygial interval is from 2 to 5 muscular articulations. The arms are all broken within 

 25 mm. distance from the caly.x. The second brachial has a convex proximal side but 

 is barely longer than the first. It bears the first pinnule, which in 6 cases (5 of wliich 

 are adjacent) is on the right side and in 4 is on the left. The distal brachials are triangular 

 and become longer than broad. 



Pi has 16+ short segments and measures 5 mm. 



Pj with 17 segments may bear a small gonad or Pj or P^ may be the first genital 

 pinnule. 



Pj has 12+ segments and measures 7 mm. The distal segments are about twice as 

 long as broad. The gonads are very short and thick; they extend for only 3 or 4 seg- 

 ments of the pinnule and end abruptly. 



