ECHINOIDEA 327 



probability of these two forms occurring so far north as the 

 British area.^ 



Key to the genera of Spatangidce represented in the British seas. 



1. Only a subanal fasciole present 



1. Spatangus (Klein) O. Fr. Miill. 



Besides the subanal fasciole also a peripetalous or an inner 



fasciole present .... .... 2 



2. An inner fasciole present ... 2. Echinocardiutn Gray 

 A peripetalous fasciole present . . 3. Brissopsis L. Agass. 



1. Spatangus (Klein) 0. Fr. Miiller. 

 (Heart-urchin.) (Syn. Prospatangus Lambert.) 



Only a subanal fasciole present. The widened part of the 

 lateral ambulacra on upper side of test (the '" petals '") scarcely 

 deepened. F'rontal ambulacrum rather deep, forming a con- 

 spicuous broad notch in anterior edge of test. Four genital pores. 

 Large, robust forms, usually somewhat unsymmetrical, the 

 right side projecting beyond the left. 



Two species in the British seas. A third species, Spatangus 

 inermis Mrtsn., is kno^^^l from the Mediterranean : it may well 

 be expected to occur also off the adjoining Atlantic coasts, but 

 there is scarcely any probability of its occurring as far north 

 as the British coasts. This species is easily distinguished from 

 the other Spatangus species by lacking the large tubercles on 

 the upper side, excepting a very few in the middle of the 

 posterior interambulacrum and on the sides of the frontal 

 ambulacrum. 2 



Key to the species of Spatangus known from the British seas. 



Test low ; subanal area about three times as broad as long 



1. Sp. purpureus O. Fr. Miill. 

 Test high ; subanal area not twice as broad as long 



2. Sp. Raschi Loven 



^ Descriptions and figures of these two forms are found in Koehler's 

 Echinodermes, Faune de France, p. 133 {Brissus unicolor), and Th. Mortensen, 

 Die Echiniden des Mittelmeeres (" Mitt. Zool. Stat. Neapel," 21, 1913, p. 32, 

 Taf. 3, o {Plagiohrissus (Metalia) Costce). 



2 Full description and figures of this species are given in Th. Mortensen, 

 Die Echiniden des Mittelmeeres ("Mitt. Zool. Stat. Neapel," 21, 1913, 

 p. 24, Taf. 1). 



