364 



posed of cellular substance, and was surrounded by vibratory- 

 cilia. Acentral transparent channel, probably the alimentary 

 tube under its most simple form, was seen extending the whole 

 length of the body. 



This is the first example that I know of, among marine plana- 

 riae, of a species bringing forth living young. We have in this 

 vicinity, Planaria gracilis Hald. {Phagocata gracilis^ Leidy,) a 

 fresh water type, in which the same phenomenon of generation 

 is observed. The organization of Planarise in general, and of 

 these two types in particular, which I am now tracing, will con- 

 tribute to elucidate the doubtful questions of their physiology 

 and their embryology. 



The first three species of the following EcJiinoderms, (two of 

 which, constituting two new genera, are described hereafter,) 

 belong to the group of true Echini, the fourth to EcJiinometri, 

 the fifth to Clypeastri, and the sixth to Spatangi. 



Genus Heliechinus Girard. 



This genus is characterized by having both the ambulacra! 

 and interambulacral spaces of the same width. The pores of the 

 ambulacra are disposed in pairs in three vertical series, the inner 

 one irregular, and interspersed with tubercles of the third magni- 

 tude. The tubercles themselves are neither perforated nor cre- 

 nated, and are a little larger on the interambulacral spaces. 

 The mouth is small and notched. The auricles are distant, and 

 the two pillars united at their summit. It difl^ers from Amhly- 

 pneustes by the absence of holes at the angles of the plates and 

 by the presence of notches at the circumference of the mouth ; — 

 from Holopneustes by having the ambulacral spaces equal, if 

 they do not surpass, in width, the interambulacral spaces, and 

 by narrower zones of pores. This genus represents, in our 

 epoch, the extinct group of Echinopsis, from which it differs 

 by the imperforate condition of its tubercles, and by the 

 arrangement of the pores in the ambulacra. There are two 

 types among Echinopsis^ a cretaceous and a tertiary type. The 

 first and oldest has a single and vertical pair of pores, whilst the 

 other possesses three oblique pairs. Should the arrangement of 

 the pores prove not to be of generic value, my genus Helie- 



