474 ECHINODERMATA ASTEROIDEA chap. 



small Starfish with short stout arms ; there are no straight 

 pedicellariae, and only a few sharp spines on the dorsal surface. 



On the eastern coast of North America there are several 

 species of Asterias, of which the most noteworthy is the 6- 

 rayed A. polaris of the Gulf of St. Lawrence. This species 

 exhibits a marvellous range of colour-variation, ranging from 

 bluish-violet through purple to red and straw-coloured. This 

 variation seems to show that colour, as such, is of no importance 

 to the animal, but probably depends on some compound of 

 slightly varying composition which is being carried by the 

 amoebocytes towards the exterior. On the Pacific coast there is 

 a rich fauna of Starfish, among which we may mention as members 

 of this family Asterias ochracea, a large violet species, so strong 

 that it requires a severe wrench to detach it from the rock, and 

 Pycnopodia with twenty-two arms. 



Fam. 2. Heliasteridae. — Forcipulata allied to the Asteriidae, 

 but with very numerous arms and double interradial septa. 

 Heli<ister. 



Fam. 3. Zoroasteridae. — Forcipulata with the tube-feet in 

 four rows at the base of the arm, in two rows at the tip. Aboral 

 skeleton of almost contiguous plates bearing small spines or 

 flattened scales. Zoroaster, Pholidaster. 



Fam. 4. Stichasteridae. — Forcipulata with the tube-feet in 

 four rows. Aboral skeleton of almost contiguous plates covered 

 with granules. Stichaster, Tarsastcr. 



The Stichasteridae and Zoroasteridae have acquired a super- 

 ficial resemblance to some of the long-armed Valvata, from which 

 they are at once distinguished by their pedicellariae. It would 

 be exceedingly interesting if more could be found out concerning 

 the normal environment of these animals ; it might then be 

 possible to discover what is the cause of the assumption of this 

 uniform mail of plates. 



Fam. 5. Pedicellasteridae. — Forcipulata with two rows of 

 tube-feet. The aboral skeleton bears projecting spines surrounded 

 by cusliions of straiglit pedicellariae. Pcdicellaster, Coronaster. 



Fam. 6. Brisingidae. — Forcipulata with numerous arms and 

 only two rows of tube - feet. Aboral skeleton largely rudi- 

 mentary and confined to the base of the arms. The small blunt 

 spines are contained in sacs of skin covered with pedicellariae. 



The Brisingidae, including Brisinga and Odinia, are a very 



