99 
[Fewkes. 
the mouth parts, still the homology of the mouth parts is the most 
important feature in this classification which is based on the char- 
acter of these oral plates. 1 
Asterina belongs to that group of starfishes which is said to have 
an adambulacral mouth, while Asterias has the calcifications around 
the mouth formed by an ambulacral and adambulacral oral ring. 
It is, therefore, an object of this paper to show that the mode of 
origin of the mouth plates 2 in both these genera is similar, and 
that such a division does not hold good in younger stages of two' 
representative genera. 
View of one arm of Asterina from the actinal side showing the relation of the 
calcareous plates; a , Ambulacrals ; ad, Adambulacrals; ado, Orals; 6, Genitals; dl, 
Dorsolateral s; d, Dorsals; to, Marginals; o, Odontophores; t. Terminal; sp, Spines. 
The above figure represents an arm of an Asterina older than 
Ludwig’s (fig. 106) in which we have represented the oral adam- 
bulacrals, ado , two pairs of ambulacrals, a, or ambulacral rafters, 
and the beginning of a third pair of these last mentioned calcifica- 
1 The Asteriae Ambulacrariae are said to have ambulacral mouth plates, pedunculate 
pedicellariae, and ambulacral pores in two rows. 
The Asteriae Ad ambulacrariae are said to have adambulacral mouth plates, sessile 
pedicellariae, and ambulacral pores in a single straight line. See Viguier (Ann. Zool. 
Exp. et Gen. vn, 1878). 
2 I refer to the plates which surround the mouth and not to the odontophores alone, 
which are sometimes homologized with the orals. 
