THE "PORCUPINE" AND "LIGHTNING" TTJNICATA. 227 



The branchial sac has the folds (Plate XXXVI. fig. 9) better developed than 

 in Poly car-pa pusilla. In one sac examined the arrangement, starting from the 

 dorsal lamina along the right hand side, was — one row of wide meshes con- 

 taining 8 to 10 stigmata, then the 1st fold with 12 bars, then the 1st interspace 

 with 2 bars, then the 2nd fold with 7 bars, then the 2nd interspace with 2 bars, 

 then the 3rd fold with 7 bars, then the 3rd interspace with 3 bars, then the 4th 

 fold with 6 bars, and then a row of wide meshes separating the ventral fold from 

 the endostyle. Figure 10 on Plate XXXVI. shows the narrow dorsal lamina 

 and the wide row of meshes separating it from the commencement of the first 

 fold on the left side of the sac. A large number of fine muscle fibres are 

 present in the branchial sac, chiefly in the transverse vessels. 



The peritubercular area (Plate XXXVI. fig. 2) is large and triangular in 

 shape. It is almost perfectly symmetrical. The tubercle is very different 

 from that of Polycarpa pusilla. It is comparatively simple, since the slit, 

 though irregular in shape, is not curved to form horns or spirals (see Plate 

 XXXVI. fig. 11, d. t.). The polycarps are irregularly rounded ; they are herma- 

 phrodite. Endocarps are not numerous. 



Polycarpa pomaria, Savigny. 



Twelve moderately large specimens of this common species were dredged 

 on August 4, 1869, near Belfast, at a depth of 70 fathoms. The largest indi- 

 vidual measures 3 cm. in length and 2 cm. in breadth. 



Three or four of the specimens differ somewhat in appearance from the 

 rest ; their tests are thinner and smoother, but otherwise they appear to be 

 exactly the same. 



A single individual of this species was also obtained in 1870 in Tangier Bay 

 from a depth of 35 fathoms. The test is stiff, giving a solid appearance and 

 feel to the specimen, and the exterior is somewhat incrusted with sand. The 

 difference in external appearance between this individual and those with smooth 

 thin tests from near Belfast is very considerable, but the species is a variable 

 one, and intermediate forms are common. 



Polycarpa formosa, n. sp. (Plate XXXVI. figs. 1-6). 



External Appearance. — The body is elongated antero-posteriorly, and varies 

 from pyriform to oblong in shape. There is almost no lateral compression, and 

 attachment is by the posterior extremity. The anterior end is moderately 

 wide, but narrower than the middle of the body. The posterior end is narrower 

 than the anterior. The widest region is usually a little behind the middle of 

 the body. The apertures are both anterior, and not distant. They form slight 

 papilla?, and are each distinctly four-lobed. 



The surface is even, but considerably incrusted with sand grains, especially 



VOL. XXXII. PART II. 2 O 



