A MONOGRAPH OF THE EXISTING CRINOIDS 181 



Pi is composed of about 25 segments the lowest of which are broad with their inner 

 edges a little cut away and the outer sides slightly flattened. The pinnules of the next 

 pair are much smaller, and those following gradually increase in length; in these the 

 lower segments are at first broadly V-shaped, later more elongated. From about the 

 twelfth brachial onward the pinnules have the third and next following segments 

 expanded for the protection of the gonads, having a broadly V-shaped cross section, 

 though this is less marked than in Th. gracilis. In the specimen with two IIBr 4(3 + 4) 

 series Pi consists of rather massive segments with their inner edges cut away a little 

 and the outer sides flattened. It is much larger than its successors. 



The disk is 4 mm. in diameter and is well plated. Side plates are fairly well 

 developed on the pinnule ambulacra, and sacculi are moderately abundant. 



The color in alcohol is light brownish white. 



Notes. — In the youngest of the three immature individuals not only the basals, 

 but also portions of the radials are concealed, and the pinnules of the first two pairs 

 have appeared, though from the sixth to the thirteenth brachials the arms are devoid 

 of pinnules. In an older individual the radials are only just visible externally, though 

 the IBri are relatively much longer than in the mature form. All the brachials are 

 provided with pinnules, although the lowest ones are quite small, Pi being much more 

 like its successors than in the adult, while there is but little trace of any expansion in 

 the lower segments of the genital pinnules. 



The spines on the cirri are present from the first, but those on the division series, 

 arms, and pinnules do not appear until after the pentacrinoid stage, while the lateral 

 flattening of the radials and lower brachials is one of the last characters to make its 

 appearance. 



Locality. — Challenger station 344; south Atlantic near Ascension (lat. 7°54'20" 

 S., long. 14°2S'20" W.) ; 768 meters; volcanic sand; April 3, 1876 [P. H. Carpenter, 1888, 

 1891;Hartlaub, 1895, 1912; Lang, 1896; Minckert, 1905; A. H. Clark, 1907, 1908, 1909, 

 1911, 1913, 1918, 1923, 1929; Gislen, 1928, 1934] (2, B. M.). 



History. — This species was described and figured under the name of Antedon 

 multispina by Dr. P. H. Carpenter in his report upon the comatulids of the Challenger 

 expedition published in 1888. The description was based upon four broken individuals 

 from station 344. The three pentacrinoid larvae also secured at this station and con- 

 sidered by Carpenter as belonging to this species possibly represent Crotalometra por- 

 recta (see Part 2, p. 521, pi. 34, figs. 1207-1209). Antedon multispina was first described 

 in the Basicurva group, and the only locality given was station 344. A supplementary 

 description, with additional figures, was given under the Granulifera group, which was 

 based upon a single mutilated specimen from station 135G. This specimen is herein 

 regarded as representing a different species, Th. setosa (see page 182). 



In a discussion of Antedon (Stiremetra) lusitanica published in 1891 Carpenter 

 compared the occurrence of a syzygy between brachials 1+2 on arms arising from a 

 IIBr 4(3 + 4) series with the condition in Antedon (Thalassometra) multispina and in 

 Antedon (Crotalometra) porrecta. He said that multispina "like Antedon lusitanica, may 

 sometimes have no more than ten arms, as in the six 'Challenger' specimens from Ascen- 

 sion; while the single individual from Tristan DAcunha [=Th. setosa] possesses one 

 bidistichate [IIBr 2] and two tridistichate [IIBr 4(3 + 4)] series, two of the arms borne 

 on the latter having a syzygial union between the first two brachials, while the other 



