PART 5 A MONOGRAPH OF THE EXISTING CRINOIDS 629 



Bathymetrical range. — From 130 (93) to 567 meters. 



Thermal range.— From —1.90° to —0.31° C. 



Salinity range. — From 33.89 to 34.85 parts per thousand. 



ISOMETRA JOHANNI sp. nov., A. M. Clark* 



Figure 35 



Isometra graminea (not /. graviinea John, 1938) John, Rep. B.A.N.Z. Antarctic Res. Exped. 1929-31, 

 ser. B, vol. 4, pt. 6, 1939, p. 191 (listed), pp. 206-207 (stations; description; pentacrinoid larva). 



Diagnostic Jeatvres. — The cirri are about XXV with the fourth and fifth of the 

 21 to 33 segments about twice as long as their median width, distincth- constricted in 

 the middle and flared distalh'; the division series and proximal brachials have a keellike 

 ridge in tlic dorsal midline; P2 is smaller than Pj, which has 9 to 11 segments; the first 

 genital pinnule is P5 or Pe. 



Pesmph'on.— Holotype B.M. reg. no. 1948.1.7.197, B.A.N.Z.A.R.E. station 40. 



The arms are about 50 mm. in length. From the proximal edge of the IBri to 

 the second sj'zygy is 9.0 mm. and the width at the first syzygy is 1.3 mm. 



The conical centrodorsal is 2.1 mm. in basal diameter and 1.7 mm. in vertical 

 height. 



The cirri are about XXV, up to 12 nun. long, with 21-33 segments, of which the 

 longest, the fourth and fifth, are twice as long as broad. The longer segments are 

 also notable in having a narrowed waist from which they flare out towards the distal 

 end. The first three segments are not conspicuously heavier than the others. On 

 the distal segments which are shorter, there is a dorsal crest but no distinct spine. 



The division series and the proximal brachials are distinctly carinate, particularly 

 the first two brachials. The keels of each pair of arms fuse at the axillary. The first 

 four brachials have very straight sides. Beyond them the arm rapidly narrows. 

 The brachials between the first and second syzygial pairs each have a markedh' raised 

 triangular area in the midline of the distal edge. The brachials bc3-ond have strongly 

 everted and spiny distal edges. 



Pi is very long and slender, its tip extending distally as far as that of P2. P, has 

 11 segments and measures 5 mm. in length, while P2 has 7 or 8 segments and is only 

 3 mm. long. In the paratypes these pinnules have similar relative proportions (see 

 table 15, on p. 620). It appears that Pi is regularly at least half as long again as Pj 

 and has at least two more segments. 



The first genital pinnule is usuafly P5, sometimes Pa on odd arms. The last is 

 Pio-12. The holotype is a female with the third and fourth segments of the genital 

 pinnules abruptly and conspicuously expanded. The brood pouches of the females 

 contain two or three embryos and a small number of eggs. There were no embryos 

 with skeletal plates among those examined. 



The pinnule ambulacra are lined with side and cover plates similar to those of 

 graminea and the tentacles contain knobbed spicules. 



The type carries a pentacrinoid larva on a cirrus. 



Pentamnoid larvae.— Dv. John described two larvae from B.A.N.Z.A.R.E. station 

 107, of which the larger has about 23 brachials on each arm. The first columnal 

 (centrodorsal) bears three whorls of cirri, the longest of which have 12 to 13 segments 



* Sec also scatter diagram (p. 83.5). 



