REPORT ON THE TUNICATA. 231 



on the sides, the dorsal edge being entirely free from them, as in Hypobyihius moseleyi. 

 In some places on the sides they are placed very closely, and have a curiously undulating 

 course (PI. XX XVII. fig. 3). 



The longitudinal arrangement of the chief bands of the musculature recalls the twelve 

 or fourteen parallel and longitudinally running muscle bands in the allied genus Ciona, 

 and also the usually longitudinal arrangement of the musculature in the Ckvelinidae. 



The branchial sac is the most remarkable characteristic of Hi/pobyt/iius, and distin- 

 guishes it from all other Simple Ascidians. There are no folds, and there are no internal 

 longitudinal bars, a condition which is only equalled in simplicity by the sac in the genus 

 Clavelina. Only a single system of vessels can be recognised, branching and anastomosing 

 so as to form a close network (PI. XXXVII. fig. 4), the small rounded meshes of which 

 are the stigmata. The tentacles and dorsal lamina cannot be made out. 



The viscera form an elongated compact mass along the dorsal edge of the branchial 

 sac (PL XXXVII. fig. 1). The alimentary canal is simple, forming a U shaped loop open 

 anteriorly. This seems at first sight an abnormal arrangement, but if the intestine 

 (fig. 1, r.) be pulled more to the left and ventrally (towards the right hand side of the 

 figure), so as to lie upon the left side of the branchial sac, the relations of the parts of the 

 alimentary canal will be found to be much the same as those in Ascidia, or any other 

 typical Simple Ascidian. 



The globular ovary and the ramified testis lie together in the intestinal loop, between 

 the stomach and the intestine, and the oviduct and large vas deferens (called by Moseley 

 the tubular testis) run anteriorly alongside the rectum, and on its right hand side, which, 

 if the intestine be pulled ventrally, as suggested above, would become the dorsal side, the 

 normal position of the genital ducts in the Ascidiidae. 



One specimen, somewhat damaged, was obtained by the trawl in the North Pacific Ocean, 

 at Station 248 ; July 5, 1875 ; lat, 37° 41' N., long. 177° 4' W.; depth, 2900 fathoms; 

 bottom temperature, 1°"1 O; bottom, red clay, with concretions of peroxide of manganese. 



Hypobyihius moseleyi, n. sp. (PI. XXXVII. figs. 6-9). 



External Appearance. — The body is of an elongated pyriform shape, compressed 

 laterally, and attached by the posterior end. The anterior end is broad and slightly 

 rounded ; the posterior is narrow, produced, and tapers to the small terminal area of attach- 

 ment. The dorsal and ventral edges are long, and converge posteriorly from the end of the 

 wide anterior extremity. The apertures are both anterior, large, and open, but sessile, and 

 apparently not lobed ; the branchial is near the ventral edge of the anterior end, and is 

 directed anteriorly; the atrial is at the anterior extremity of the dorsal edge, and is 

 directed anteriorly and slightly dorsally. 



The surface is smooth all over. The colour is yellowish-grey, pale brown in parts. 



Length of the body, 9 cm.; breadth of the body, 4 cm. 



