REPORT ON THE TTJNICATA. 191 



one-third of the way from the anterior to the posterior end, and on the left side, not 

 far from the dorsal edge. Both apertures are sessile and inconspicuous. 



The surface is slightly rough, especially at the anterior end ; it is generally prolonged 

 here and there at the edges and the lower surface into fine hair dike branched processes. 

 The colour is dull grey. 



Length of the body, 3 cm.; breadth of the body, 1 cm. 



Tlie Test is thin, but moderately strong ; no vessels are visible 



The Mantle is very delicate over most of the right side and half of the left, while on 

 the anterior and dorsal edge of the right side, and the anterior half of the left side 

 muscular bands are extraordinarily developed, and attain a great thickness (up to 0'3, and 

 in one or two cases 0'5, mm.). The siphons are muscular and fairly prominent. The 

 branchial aperture is provided with eight, and the atrial with six ring-shaped ocelli, of a 

 light rust colour. 



Tlie Branchial Sac is not plicated. The transverse vessels are large and are all equal 

 in size. They are joined by short wide longitudinal vessels, thus forming square meshes 

 in which the spirally coiled secondary or interstigmatic vessels lie. Internal longitudinal 

 bars are numerous, being in excess of the wide longitudinal vessels. They are delicate 

 but distinct, and are united to the transverse vessels by wide horizontal membranes, 

 which are present in the proportion of two or three to every transverse vessel. The 

 stigmata are curved, and are placed spirally, in rows of square meshes separated by the 

 transverse vessels. The stigmata near the outside of the mesh are usually crescentic, 

 whde those further in are longer and are coiled spirally. 



Tlie Dorsal Lamina is represented by a series of long tapering languets. 



The Tentacles are very numerous, touching at their bases ; they are all of one size, 

 and are moderately long and filiform. 



The Dorsal Tubercle is regular, the outline is between cordate and ovate, and both 

 horns are coiled inwards. 



The Alimentary Canal is moderately large, and is placed on the right side of the 

 branchial sac. The stomach is nearly globular. The intestine is wide, and curves round 

 ventrally and posteriorly to the stomach. 



The Genitalia are on the first part of the intestine, and in the intestinal loop. 



This species, which agrees in all generic characters with Coretta as defined by Hancock 

 in 1870, is the only species collected during the Challenger expedition which can be 

 referred to that genus. 



The general form of the body distinguishes this species clearly from Corella parallelo- 

 gramma, 0. F. Midler ; Corella minuta, Traustedt ; Corelhi larvceformis, Hancock; and 

 Corella ovata, Hancock. It is more nearly allied to Corella eumyota, Traustedt, but may, 

 I think, be distinguished from that species also by several details of structure. In Corella 



