266 HERBERT C. CHAD WICK. 



The abnormal character and displacement of the anus and the canal- 

 like ambulacrum are not so easily accounted for ; but they are minor 

 points, and do not appear to me to impair the value of what has been 

 advanced above. 



EXPLANATION OF PLATE XIII. 



List of reference letters. 



a. Anus. g. Gut of supernumerary disk. 



a.g. Ambulacral grooves. in. Mouth, 



c. Abnormal ambulacrum. r.iv.v. Radial water-vessel. 



c.w.v. Circum-oral water-vessel. s.d. Supernumerary disk. 



f.p. Funnel-shaped projection of s.o. Skeletal ossicles. 



supernumerary disk. w.t. Water-tubes. 



g. Gut. x. Ambulacral groove. 



Fig. 1. Oral surface of abnormal specimen of Antedon rosacea, x 5. 



Fig. 2. Aboral surface of abnormal specimen of Antedon rosacea, x 5. 



Fig. 3. Sagittal section through the normal and supernumerary disks, show- 

 ing the point of union of the two, x 16. 



Fig. 4. Sagittal section of the supernumerary disk, passing through the 

 mouth and anus, x 16. 



Fig. 5. Sagittal section of the supernumerary disk, showing the funnel- 

 shaped projection traversed by the abnormal ambulacrum, x 16. 



