VAN NAME: SIMPLE ASCIDIANS. 525 
widely separated. The body surface bears numerous and very 
characteristic large spinous processes, which at once serve to dis- 
tinguish the species from all other ascidians of the New England 
region. Each process has the form of a stout tapering column at the 
summit of which an irregular circle of tapering branches, usually four 
Text-fig. 23. — Pyura echinata (Linnaeus). X 3. 
to eight in number, arises. Some of the branches may fork once. 
One of them may have a central position, the others extending out 
radially from around the base, or all may extend out radially or 
obliquely. Both the main stem and these branches are studded with 
slender hair-like spines of varying length (see fig. 65). These 
spinous processes exceed the siphons in length in the contracted speci- 
mens. The largest specimens examined measured about 22 mm. long, 
14 mm. high, dorso-ventrally, and 15 mm. from side to side. 
Color "usually deep salmon, often more or less tinged with pink 
or flesh-color, and sometimes of a delicate flesh-color throughout. 
The apertures are red, often bright red with a lighter red ring; the 
tubes frequently have eight alternate light and deep red longitudinal 
stripes extending from the edge to the base of the tubes, or four light 
stripes extending from the angles of the apertures down their sides " 
(Verrill, 1871a, p. 96). Test of moderate thickness and very tough. 
Mantle very thin and generally so closely adherent to the test that 
it can be removed in small fragments only. Musculature not greatly 
developed. About the origin of the siphons the radial and circular 
muscles form distinct though rather narrow bands, the circular ones 
being the more superficial. 
Tentacles of four or five orders, arranged with some degree of 
regularity; the largest extensively branched in an irregularly pinnate 
manner, twice compound (to a small extent three times), the main 
