CRINOIDEA 17 



I. Family Bathycrinid^ 



(Syn. Bourgueticrinidce auct.) 



Stalk slender, consisting of elongate joints with elliptical 

 articular surfaces, those of the two ends of each joint at an angle 

 to each other. The upper stalk-joint not specially developed, 

 new joints constantly forming under the calyx. No true cirri, 

 only root -like, branching ajopendages in the basal part of the 

 staik. 



The sea-lilies of this famil^^ are very liable to throw off their 

 arms ; specimens with the arms regenerating are therefore often 

 met with. 



Two genera of this family are known from the British seas. 

 It is, however, very probable that three (four) more genera 

 will ultimately be found to occur there, namely — besides llycriniis 

 Dan. and Kor. (see below, p. 20)^ Bathycrinus Wyv. Thomson, 

 the species B. gracilis Wyv. Thomson being known from off the 

 Bay of Biscay, 4450 m. ("' Porcupine ") ; Monachocrinus A. H. 

 Clark, with~three N.E. Atlantic species (cf. below, p. 21), and 

 BytJwcrimis Doderlein,^ the species B. robustus (A. H. Clark), 

 being known from off the coast of Portugal, the Josephine Bank, 

 and the West Indies, ca. 160-1745 m. These genera are therefore 

 included in the following ke}^ : 



Key to the genera of BathycrinidcE known from or likely to occur 

 in the British seas. 



1. Muscular and non -muscular (ligamentous) articulations alternating 



regularly throughout the arm (Fig. 6, 1). 5-10 (4-12) arms 2 



5th, 8th and 1 1th joints, counted from the radials, have a muscular 



articulation at either end (Fig. 6, 2). 10 arms . . 5 



2. 10-12 arms, each radial bearing two arms Monachocrinus A. H. CI. 

 5 (4-7) arms, each radial bearing only one arm ... 3 



3. Basals fused into a solid conical ossicle ; no sutures between the 



basals (Fig. 6, 1). 4-7 arms . . 1. Rhizocrinus "SI. Sars 



Basals separated by distinct sutures (Fig. 6, 2). 5 arms . 4 



4. Stalk relatively slender, longest joints at least twice as long as 



broad ; calyx more or less conical . Bythocrinus Doderlein 



Stalk rather stout, the longest joints usually only slightly longer 



than broad, rarely so much as twice as long as broad. Calyx 



almost or quite cylindrical . . 2. Democrinus Perrier 



^ The genus Bythocrinus should perhaps rather be united with 

 Democrinus. 



