MUSEUM OF COMPARATIVE ZOOLOGY. 213 



DESCRIPTION OF A YOUNG HOLOPUS. 



A VERY young specimen of Holopus was dredged in the " Blake " Ex- 

 pedition in Lat. 23° V N., Long. 83° 14' W. Depth 100 fathoms. It 

 has been sent to Professor Sir AYyville Thomson for study, but was pre- 

 viously drawn by Mr. Agassiz for the accompanying plate. 



The specimen is attached to a piece of rock, and was not detected 

 until it had become dry. The general shape is a truncated cone when 

 contracted, with irregular contour of attachment. The body part is 

 very short, spreading out a little at the foot ; surface granulated or 

 shagreen-like, with a few small tubercles scattered over it. No trace 

 of divisions can be detected in this part. Above, there are two circles of 

 five plates each, fitting closely together and concealing the arms entirely. 

 The lower plates are pentagonal with rounded corners, the upper and 

 lower sides being parallel. The lower sides do not form a continuous line 

 from plate to plate, so that there are small triangular spaces left be- 

 tween them. There is a row of tubercles on each side of a plate, and 

 one in the middle forming a ridge which projects a little downward over 

 the lower edge of the plate. On the upper edge of these plates are 

 articulated five smaller triangular ones, firmly closed together. They 

 have also a ridge in the middle in continuation of the ridge in the lower 

 plates. The larger pentagonal plates are the radial axillaries of Sir 

 Wyville Thomson, but the smaller triangular ones seem to become fused 

 with them in the adult. Color black. Diameter at base 3 mm., height 

 a little over 1 mm. 



Plate II. 



Young Holopus from above and in profile, magnified about eighteen 

 diameters. 



