196 ZOOLOGY. 



tens of the sand -stars, the bipinnaria (Fig. 138) of certain 

 star-fishes, and the auricularia of the Holotliurians. 



Fig. 139 shows the star-fish developing on the aboral end 

 of the brachiolaria, whose body it is now beginning to ab- 

 sorb. The brachiolaria soon shrinks, falls to the bottom, 

 and attaches itself by its short arms. The star-fish com- 

 pletely absorbs the soft body of the larva, and is conical, 

 disk-shaped, with a crenulated edge. In this stage it re- 

 mains probably two or three years before the arms lengthen 

 and the adult form is assumed. 



In Leptychaster kerguelenensis Smith, of the South Paci- 

 fic, a form allied to Luidia or Ar chaster, the young develop 

 directly in a sort of marsupium, according to Wyville- 

 Thompson. Pteraster militaris was found by Sars to be 

 viviparous. 



In Brisinga the arms number from nine to twenty, are 

 long, cylindrical, and, like the body, bear long spines. The 

 species are abyssal. B. endecacnemos Asbjornsen lives on 

 the Norwegian coast, at a depth of about 200 fathoms, and 

 was dredged in abundance by the Challenger Expedition in 

 1350 fathoms, at a station due south of St. George's Banks, 

 associated with other species of star-fish (Zoroaster and As- 

 tropecten), and again in eighty fathoms on La Have Bank, 

 off Nova Scotia. A common form living in mud in usually 

 from ten to thirty fathoms is Ctenodiscus crispatus Retzius, 

 in which the body is almost pentagonal, the arms being very 

 short and broad. Arcliaster is a genus of star-fishes occurring 

 at great depths, A. vexillifer Wyville-Thompson (Fig. 140), 

 occurring off the Shetland Islands, in from 300 to 500 fath- 

 oms. Luidia is called the brittle star-fish, as when brought 

 up from the bottom and taken out of the water it breaks up 

 into fragments. It has five long arms. L. clathrata is com- 

 mon on the sandy shores of the Carolinas, and ranges from 

 New Jersey to the "West Indies. Astropecten articulatus 

 (Say) has the same range. Astrogonium phrygianum Parel 

 is a large pentagonal, bright-red star-fish, living in twenty 

 to fifty fathoms on rocky bottoms in the Gulf of Maine 

 and northward ; while Pteraster militaris Miiller is an 

 arctic species which ranges south to Cape Cod. It is sub- 



