Cj-athocormus mirabilis n. g., n. sp. 13 



of Diplosomoides lacazel Giard in following words : "La paroi 

 péribranchiale, fort réduite, laisse la branchie presque entièrement 

 à découvert ", and this is exactly what takes place in our species, 

 though very probably we have here a case of convergence rather 

 than that of a direct phylogenetical affinity. The posterior limit 

 of the thorax is marked for the most part by the bottom of the 

 branchial sac, at one point of which the funnel-shaped oesophagus 

 commences. The terminal portion of intestine lying just beneath 

 the branchial sac is also comprised in the thorax (PL II., fig. 8). 



The abdomen is irregularly ellipsoidal and somewhat flattened 

 from side to side. Its shape is determined principally by that of 

 the intestinal loop, since the heart and other organs contained in 

 the abdomen are all placed between the stomach and ascending 

 part of the intestine. As the investing mass as well as the thin 

 body-wall is perfectly transparent and colourless, the external 

 form of the abdomen is hardly recognizable to the naked eye, 

 while the intestine itself is rendered very conspicuous by its dark 

 coloured contents. The vascular appendage, whose lumen is 

 continuous with the blood spaces of the zooid, starts from the 

 posterior end of the abdomen and runs, as will be more minutely 

 described hereafter, inwards and dow^nw^ards through the common 

 investing mass to the base of the colony. 



Body ivall. The body w'all or mantle forms the outer covering 

 of zooids and lies immediately under the test, with which, however, 

 it is in the greater part of its extent not closely connected. In 

 preserved specimens a cavity in which the zooid lies is distinctly 

 visible (PI. I., fig. 3; PL IL, figs. 7, 8; PL IIL, fig. 20, sp.). In 

 the living animal, however, when the contractile tissues were 

 relaxed and the viscera were filled with water, the body Avail was 

 doubtless in contact with the test throughout, and there was 

 therefore no cavity around the zooid. In those places where the 

 test ends with a free margin, the body w^all is more firmly 

 attached to the test and remains closely connected with it even 

 when preserved. Such places are found at the base of the branchial 

 siphon and along the border of the body wall in the thoracic 

 region. 



