THE " PORCUPINE " AND " LIGHTNING " TUNICATA. 221 



as being usually transversely elongated, and as containing each about twelve 

 stigmata; but in some of the "Porcupine" specimens the meshes are occa- 

 sionally square, and have only 6-7 stigmata. Here and there at the angles of 

 the meshes very short hemispherical papillae may be found on the internal 

 longitudinal bars, otherwise the " Porcupine " specimens agree with the 

 description and figure in the Journal of the Linnean Society. 



The large tentacles are rather stouter than those in my former figure, # but 

 the arrangement is the same. The dorsal tubercle is somewhat variable in 

 this species, but is always very simple. Two of the " Porcupine " specimens 

 have it intermediate in shape between those figured by myself in 1880 1 and 

 by JulinJ in 1881. 



In several of the specimens large masses of ova are present in the peri- 

 branchial chamber. 



Ascidia plebeia, Alder, var. nov. {X) (Plate XXXV. figs. 1-3). 



External Appearance. — The body is irregularly ovate or pyriform, greatly 

 compressed laterally, and attached by the posterior half, or more, of the left 

 side. The anterior end is narrow and produced, the posterior considerably 

 wider. The dorsal and ventral edges are irregular, but nearly equally curved; 

 both sides are flattened. The branchial aperture is terminal and prominent; 

 the lobes are well marked. The atrial aperture is from one-third to half way 

 down the dorsal edge, prominent, projects laterally, and has well-marked 

 lobes. 



The surface is somewhat irregular, but not rough. There are adhering sand 

 and shell fragments at the posterior end and over part of the left side. 



The colour is yellowish- grey. 



Length of the body, 42 cm.; breadth, 1*9 cm. 



The test is moderately thick and strong, of a firm gelatinous consistency, 

 translucent, smooth, and glistening on the inner surface, and richly supplied 

 with blood-vessels. The left side and posterior end are thickened and made 

 stiff by the presence of many imbedded sand grains and fragments of shells. 



The mantle is moderately strong. The musculature is well developed on 

 the right side and the anterior end of the left, but is very slight over' the 

 visceral part of the body. The sphincters are fairly strong. 



The branchial sac is slightly plicated longitudinally. The transverse 

 vessels are all of the same size. The internal longitudinal bars are strong, and 

 bear large curved and sometimes forked papillae at the angles of the meshes, and 

 smaller simple ones between. The meshes are slightly elongated vertically, and 



* Loe. cit., pi. xvii. fig. 2. f Loc. tit., pi. xvii. fig. 1. 



\ " Recherches sur l'organisatioii des Ascidies Simples, &c," Archives de Biologie, t. ii. fasc. 1, 

 pi. iv. fig. 2. 



