Stephionson — Tlie Oenus Coratlimorphus. 17'J 



C. rigidus, Moseley. 

 (Plates XIX, XX ; text-ligr,. 1 ami 2.) 



Locality.— SR. 330. May 12, 190G. Lat. N. 51^ 1'.)'; Lniig. VV. 12'' 20'. 

 Trawl, 673-720 fathoms. 2 specimens. 



Measurements : (i) Larger Specimen. — Diaiiiw. of pedal (Hhc, 5'6 x ■4'4 cm. ; 

 oral disc, 7'0 x 6'1 cm. Length of a large tentacle, lo cm. Height of 

 body, 23 cm. Length of month, 1"75 cm. 



(ii) Smaller specimen. — Height of body, L4 cm. Diam. of oral disc, 

 3-8 cm. 



External characters. — The two specimens are photographed in PI. XIX, 

 and this shows the general appearance very well, as seen from above. I am 

 indebted to Mr. F. Culliford, of Aberystwyth, for the photograph. The 

 smaller specimen is attached to a piece of stone like coal. The body is rigid 

 and glassy ; so is the oral disc, into which the body-wall directly passes, 

 without any special margin. The mesogloea is interesting. In the oral disc 

 and most of the body-wall it is extraordinarily thick (as a glance at Y and Z, 

 text-fig. 2, will show), and is firm and semi-transparent, rather like soft 

 cartilage. In the actinopharynx and pedal disc it is not usually thick (see Z). 

 The larger specimen has the pedal disc very scarred, and smaller than the oral 

 disc, whereas in the smaller it is well expanded, and hardly if at all smaller 

 than the oral. The oral disc has not very distinct radii. The large speci- 

 men has 42 ridges and furrows on its body-wall, the furrows corresponding 

 to the mesenterial insertions, the ridges to the exo- and eudocoels. Text- 

 fig. 2, Y, shows a diagram of a transverse section of body-wall, actinopharynx, 

 and directive mesenteries in one-half of the larger animal. It displays the 

 thick wall with its ridges, and shows how the furrows correspond to mesen- 

 terial insertions. These insertions are indicated by breaks in the boundary- 

 line of the inner side of the wall, and it will also be noticed that the exocoels 

 and endocoels are often pointed in section ; the mesenteries themselves, 

 except the directives, are omitted ; they are too complicated for inclusion in 

 an outline sketch. The ridges on the body are less definite in the small 

 specimen. The oral disc is fiat and thick, and the tentacltjs pass through it 

 as tubes lined by endoderm. Text-iig. 2, Z, sliould be referred to here ; it 

 represents in outline a vertical section through one-half of the body of the 

 large specimen, passing through a directive endocoel, and thus including 

 2 tentacles, one marginal and one discal. All the tentacles, both marginal 

 and discal, consist of a shat'L and a terminal knob, the shaft being ruliier 



[A- 2] 



