8 p. HERBERT CARPENTER. 



gous with those of the young Amphiura (PI. I, figs. 12, 13), or 

 Hemipholis, and also with those of the adult Ophiorausium 

 pulchellum (PL I, fig. 9), are not mentioned as such. 



A yet more curious condition than that of these three species 

 is presented by Ophiomitra exigua (PI. I, fig. 5), which has 

 no radials at all, nothing but the five interradial basals (3) 

 intervening between the dorsocentral (1) and the radial shields 

 (r). Lyman^ describes the disc as follows: — ''Almost the 

 entire upper surface is occupied by the large triangular, 

 swollen, naked radial shields, which are joined their entire 

 length. In the centre is a small patch of irregular scales with 

 five radiating, single, interbrachial rows, and others along the 

 margin. '■* 



The condition of this type is a very singular one, the more 

 so as in other species of the genus no definite arrangement of the 

 disc plates can be determined. Basals are present (PI. I, fig. 5 ; 3) 

 and radials absent ; this being exactly the reverse of the 

 ordinary embryological condition, which persists through life 

 in so many species (PI. I, fig. 9). It would be very in- 

 teresting to know whether the radial primaries are ever 

 developed and ultimately become resorbed, or whether they 

 really never make their appearance at all. The "Blake^' obtained 

 only one specimen in 1877-78, which measures no more than 

 2*5 mm. across the disc ; but this seems to be almost too large 

 for the supposition that its radials have been greatly retarded 

 in development, and that they would have appeared ere 

 maturity was reached. Two of the " Blake " dredgings in 1879 

 yielded a type to which the same specific name is appended by 

 Lyman, but with a (?), and he gives no information about 

 them. The question, though unimportant as regards the 

 Ophiurids alone, is one of some interest in its morphological 

 bearings; for this type of "rosette" with interradial primaries 

 presents an approach to the condition of the calyx in an early 

 Crinoid larva. This may have as many as eight stem-joints 

 separating the dorsocentral from the relatively large basals by 



' "Keport on the Ophiurans obtained by the 'Blake,'" 1877-78, 'Bull. 

 Mus. Comp. Z06I.,' vol. V, No. 9, p. 231, PI. i, fig. 5. 



