NEW SPECIES OF THE GENUS COTHURNIA. 13 



The form of our species P. deprcssmn (see Figs. 33, 34) is so analogous to the 

 embryo of a Nereis, whose curious changes were studied by Loven, that I am in- 

 duced to copy the figure and description of the latter, as given in Owen's Lectures, 

 page 147. 



He says: "Dr. Loven obtained, in August, from the Baltic Sea, a discoid animal- 

 cule (as in Fig. 4, e), which rapidly moved by means of two rows 

 of vibratile ciHro; the principal row being situated upon a project- 

 ing ring {h) at the margin of the disk. It had a mouth (o) and 

 an anus (c) at the apex of the cone. The course of the aliment- 

 ary canal was detected by feeding with indigo. In a short time, 

 the cone began to elongate and to be divided into segments which 

 were developed in four parts, the two principal pieces forming half 

 rings, one on the upper, the other on the lower surface, which 

 were united by two shorter lateral pieces. Coincident with this 

 change was the development of a head from the discoid surface 

 (e), upon which the black ocelli and then two pointed filaments 

 or antennae (/) (Fig. 4, f) made their appearance. The length of the body and 

 number of segments increased, the disk and cilia still existing. The disk is after- 

 wards reduced to an appendage on each side of the head, and finally disappears. 

 The new rings are added to the front of, and not behind the old ones. The tubular 

 and setigerous feet are afterwards added." 



This account, and particularly the comparison of the above figure with the form 

 represented in the Plate, Figs. 33, 34, leads me to suspect that at least a portion 

 of the forms which are now included in the genus Perklinium, may be imperfectly 

 developed, or embryonic Annelids. 



IX. 



New Species of tue Genus Cothurnia? 



Cotliurnia ? perlepida, B. 



(Plate, Fig. 27.) 



Apex of the case attenuate, slightly curved ; surface entirely covered with spiral 

 decussating rows of hexagonal cells; orifice crenulate. Animal unknown. 



Habitat, St. George's Bank and New Haven Harbor. 



In order to give a name to the beautiful bodies above described, I have referred 

 them, although with much hesitation, to the genus Cothurnia, to the cases of which 

 they have much resemblance in shape. I have never found them in materials 

 which have been acted upon by acids, although noticed prior to the action of the 

 acid; which fact, added to the great transparency given to them by Canada Balsam, 

 in which they become almost invisible, leads me to believe that they are mem- 

 branaceous. Should they prove to be silicious, they might be referred to the genus 

 Ehizosolenia. I have seen several specimens from St. George's Bank, and also one 

 from the mud of the harbor of New Haven, Connecticut. 



