132 ASTERI.E. 



avenues are much longer, similar in form, and arranged in 

 transverse fasciculi. The mouth is guarded by a mechanism 

 similar to that seen in the Solasters ; oval plates at the 

 oral junctions of the rays, bearing four series of upright 

 spines on their surface, and a comb of about seven long 

 spines projecting over the mouth. In this species the 

 points of the five combs nearly meet, so as to form a very 

 efficient protection. Such a protection is more needed in 

 the Butthorn than in other Starfishes, as its body and arms 

 are not nearly so flexible. The extremity of each ray is 

 turned up, and presents a circle of blunt spines forming 

 the eyelid. 



This species sometimes measures six inches across ; 

 generally from three to five. Mr. Ball says it grows to 

 nine at Youghal. It is extremely variable, varying in the 

 form of the rays, in the number of border-plates, and the 

 presence or absence of spines upon them, and in colour. 

 These variations have given rise to the creation of several 

 spurious species, such as the Asterias Jonstoni, and penta- 

 cantha of Delia Chiagi, and the Asterias spinulosa, platya- 

 cantlia and subinermis of Phillippi ; perhaps, also, the 

 Asterias Mspinosa of Otto. There has been a fancy among 

 naturalists to split up the Linnsean Asterias aurantiaca, 

 which has been carried much too far. Species have been 

 founded on the breadth of the rays, — a point in which 

 every specimen differs more or less from another ; and on 

 the number of the marginal plates, which varies according 

 to age and size. The spines seen sometimes on the mar- 

 ginal plates furnish no true characters, as specimens not 

 unfrequently occur in which the plates of one ray bear 

 spines, and those of the other are naked. The form of 

 the border spines also varies exceedingly, even in the same 

 specimen. The colour, sometimes altogether brick-red 



