160 



LOWER INVERTEBRATES. 



North Atlantic. Its place in the Xorth Pacific is taken by S. decemradiata. The retic- 

 ulation of the skeleton is close, and the arms less flattened than in the next species. 



Crossaster jmppostis is common to both sides of the Atlantic, and is found in Nor- 

 way, Denmark, Britain, France, and in America as far south as Massachusetts Bay. 

 It has twelve arms, the spaces between which are largely filled up upon the oral side 

 by a membrane, while the upjier surface is an open network of limestone rods, carrying, 

 at the points of junction, club-shaped j>rocesses which bear tufts of small spines. 



Cribrelhi scx-raJi<(t((, from the Antilles, is remarkable from its possession of six 

 arms, an exceptional character in this genus. It has also the faculty of reproduction 

 by division into two halves, so that most examples show three larger and three smaller 

 anns. This jiower is also possessed by several of the many-armed Asterias, by some 

 Jji7ic/cias, aiKl some ^IsferiiiKs. Cribrella scuigainolenta is common on the Xew 

 England coast below low-water mark. 



The vVsrr.RiD.K are stai--fishes which usually have the arms well-developed, and have 



four rows of water-feet, each ending in .a 

 sucking-disc, along the ambulacra. One 

 of the largest genera is Asterias, or ^tster- 

 iiautthion, s|iecies of which are found 

 everywlu'i'c in the northern hemisphere. 

 A. rube/is is a common European form. 

 J. beri/linus extends from Halifax, Xova 

 Scotia, to Florida, while A. vulr/aris 

 ranges from Long Island Sound to Lab- 

 rador. The last two species arc both 

 (•(mimon in Blassachusctts Bay. 



In A. ochniceu, which ranges from 

 Sitka to San Diego, and is the most com- 

 mon star-fish of the Californian coast, the 

 arms and the ambulacra are wider than 

 in most species of the genus, and the cal- 

 careous netwoi-k which covers in the sides 

 and back of the arms is exceedingly solid. 

 Several other species of Asten'as occur u])on the Pacific coast of the United States, 

 but the most conspicuous is the large six-armed A. (//(/((iiteti, which attains a diameter 

 of more than two feet. Nearly allied is Pi/cnopodiu /iclutnthoides, a gigantic form 

 with more than twenty arms, common on the Pacific coast of North America, from 

 Cajie ilendocino to .Vlaska ; the calcareous skeleton of the upper surface is reduced to 

 a few small rods at the base of the sjiines, and hence a large well-presented specimen 

 is a rarity. This sjiecies attains the diameter of three feet, or thereabouts, and is of 

 a bright red color in life. Professor A. ^Vgassiz considers that this species, as well as 

 Crossaster jxipjwsits, are in many respects allied to liv!shu/a. 



The many-armed Asterida' are, for the most jiart, included in the genus Jleliaster, 

 or sun-star, two species of which, II. hubhiij! and II. luicrobraclda, occur upon the 

 west coast of North America, from Panama to Ca])e St. Lucas. The latter foi'm has 

 more than thirty arms, and the free portions of the arms are very short. 



Zoroaster fill (jei IS, dredged northwest of the Hebrides, has immensely long arms 

 and a very small disc, not one-twelfth of the total diameter of the animal, which 

 measures ten inches across. It closely resembles Ophidiaster, but has four rows of 



^""^k 









i-v*. 



'J^.ix 



Fra. 139. — .'"Vi'i'ids vulijarU 



