CHINOIDEA 39 



distal ends not expanded. The lower brachials not joining their 

 neighbours. 



Only one species found in British seas, the only known species 

 of this genus. 



1. Orthometra Jiibernica (A. H. Clark). (Fig. 23, 2.) 

 (Syn. Trichometra hibernica A. H. Clark.) 



Cirri very numerous, completely covering the centro-dorsal ; 

 short, ca. 13 mm. long, with ca. 15-33 segments. The distal seg- 

 ments have a median dorsal carina tion. The lower brachials have 

 everted and serrate distal edges. A small and delicate species. 



Colour in hfe unknown. Pentacrinoid stage unknown. 



Hitherto found only W. of Ireland ("' Helga ") and S.W. of 

 the Faroe Islands (" Ingolf "), in depths of ca. 700-1000 metres. 



7. Hathrometra A. H. Clark. 



Centro-dorsal subconical, with numerous, crowded cirrus 

 sockets. Cirri long and slender, the j)roximal joints elongated ; 

 much longer than the distal (Fig. 12, 1). Brachials not with 

 strongly produced and very spinous distal ends. Pinnule^ much 

 elongated, 2-3 times as long as Pg. 



Only one species known from British (and European) seas. 



1. Hathrometra Sarsii (Diiben and Koren). (Fig. 24.) 



(Syn. Antedon Sarsii Diiben and Koren ; A. tenella Retzius ; 

 Hathrometra norvegica A. H. Clark.) 



Cirri numerous, with ca. 20 (14-23) joints ; those on the apex 

 of centro-dorsal smaller and with fewer joints. Pinnule^ com- 

 posed of 30-40 segments ; a few of the basal segments are short, 

 the following becoming slender and greatly elongated ; Pg very 

 much shorter, with only a few joints. Colour in life greyish, 

 with indistinct, brown transverse bands. 



It is a slender and fragile species, which is very liable to 

 throw off its arms on being taken out of the w^ater ; good, 

 complete specimens are therefore rather difficult to obtain. 



The first developmental stages unknown, but probably the 

 eggs are free. The Pentacrinoids have a long and slender stalk 

 composed of up to ca. 40 very slender segments. The young 

 feather-star does not detach itself until a rather late stage, when 

 20-30 cirri have appeared and the arms have 5-6 j^innules on each 

 side (Fig. 25). 



