25 i 



NATURAL HISTORY. 



The characters of the genus Chelyosoma* are covering horny ; form oblong, depressed ; upper sur- 

 face covered by eight polygonal plates ; aperture small, six-valved, prominent. Its habitat is Greenland. 



Genus Boltenia. These Ascidians have a horny covering, and are attached by a stalk, the young 

 growing on the stem of the parent. The apertures are on the side ; they live attached to stones 

 in deep water, sometimes as much as seventy fathoms. Six species are enumerated from New 

 Zealand, Greenland, and North America ; they are most abundant in Arctic seas. 



FAMILY II. CLAVELLINID^E (SOCIAL ASCIDIANS). 



The members of this family are compound, i.e., each individual has its own heart, respiratory 

 system, and organs of nutrition, but fixed on stalks or bases common to the group, through which the 

 blood circulates in opposite directions, like the ebbing and flowing of the sea. 



Genus Clavellina.1[ The body is elongated, erect ; the covering is smooth, transparent, and 



marked with coloured lines. The individuals of a group are 

 connected or united by creeping tubular prolongations from the 

 common tunic. These are small, transparent, compound 

 Ascidians, found adhering to stones and seaweed by means 

 of curious root-like prolongations of their outer tunic, by 

 which a circulation is kept up common to the entire com- 

 munity. They are found in Great Britain, Greenland, and 

 the Mediterranean. 



Genus Perophora. The animal is stalked, roundish, flat- 

 tened, and united by pedicles to creeping root-like tubes, part of 

 the common tunic through which the blood circulates. P. 

 listeri is a minute creature, and was discovered by Mr. Lister 

 at Brighton. He says, " It occurs in groups consisting of 

 several individuals, each having its own heart, respiration, and 

 system of nutrition, but fixed on a peduncle that branches 

 from a common creeping stem, and all being connected by a 

 circulation that extends throughout." Mr. Me Andrew and 

 Professor E. Forbes dredged it adhering to weed 011 the Coast 

 of Anglesey. " It is beautifully transparent, appearing on 

 the weed like little specks of jelly dotted with orange and 

 brown, and linked by a winding silveiy thread." (Forbes.) 



The characters of the genus Syntethys are animals com- 

 pound, gelatinous, orbicular, sessile ; individuals very promi- 

 nent ; arranged sub-concentrically in the common mass ; 

 branchial and atrial orifices simple ; not cut into rays. 



Syntethys is a Clavellina with the habit of a Diazona. 



BOLTENIA (ASCIDIA) PEDVNCL-LATA. 



The only known species forms compact, greenish, translucent, gelatinous masses of half a foot in 

 diameter, and nearly equal height, affixed to rocks or stones by a short base. The individual 

 Ascidians are, when full grown, two inches in length. (Forbes and Hanley.) They are found in 

 Applecross Sound. 



FAMILY III. BOTRYLLID^E (TRUE COMPOUND ASCIDIANS). 



In the last family the individuals were seen to be connected by a common tunic, but in 

 this family, the Botryllidce, the separate envelopes are fused, and lose their individuality, forming 

 a common covering in which all the Ascidians ar? embedded, in one or more groups. Their mouths, 

 or branchial orifices, are simple, and each cluster is ranged round a common " atrial " or excurrent 

 orifice. 



If when walking on the sea-shore about low-water mark we turn over large stones, or look under 

 projecting eaves of rock, we are almost sure to see translucent jelly-like masses of various hues 

 of orange, purple, yellow, blue, grey, and green, sometimes nearly uniform in tint, sometimes beauti- 

 fully variegated, and very frequently pencilled as if with stars of gorgeous device ; now encrusting the 



* Greek, chelys, a tortoise ; soma, body. f Latin darclla, a small staff. 



