THE OSTEACODA. 229 



Group of Species. 



rotundata rotundata. 



pusilla, var. major. 



curta curta = stigmatica. 



bispinosa Haddoni. 



loricata loricata=ctenophora. 



magna magna = macrocheira. 



hyalophy Hum = lopliura. 



spinirostris = porrecta. 



zetesios, sp. n. 

 mollis kampta. 



tyloda. 



rhynchena. 

 imbricata imbricata. 



ametra. 

 daphnoides daphnoides = lacerta. 



Only four of Miiller's fifteen groups were not represented, those of dentata, acuminata, 

 ohtusata, and alata. 



CONCHCECIA AMETRA, Miiller. 



(Plate 16. figs. 1-19.) 



The sizes of this species were given by MiiUer (p. 118) as : $ 4'l-4'6, 6 3'7-4"l. 

 Measurement of his figure shows that he included the rostrum and posterior spine in 

 these lengtlis ; this figure, measured in the manner adopted in the present memoir, 

 gives a length of 3"5 for the female ; his specimens were therefore at the same stage as 

 my longest specimen, as also apparently were those of Vavra and Juday. There is 

 probably an older stage not yet captured, since the next lowest stage (mean 2-16) had 

 not developed secondary male sexual characters. 



Stage II. 



Male (Mean 310). — Shell elongate; the height about half the length; with a 

 marked shoulder-ridge. The dorsal border of both shells terminates posteriorly in a 

 single spine, the left being longer than the right ; the posterior border begins nearly at 

 right angles to the dorsal border ; the postero-ventral angle rounded off. The ventral 

 border is slightly arcuate, and docs not begin to taper till well in front of the middle of 

 the length; the shell is about equally higli in front of and behind the arcuation. 

 Rostra of the general type of the ivibricata-group, but shorter than in imbricata ; they 

 are asymmetrical, the left being longer than the right. A papilla which carries the 

 openings of the glands of the right side is large, and projects markedly beyond the shell- 

 outline ; that of the left side is small, and projects little or not at all. Sculptui-e of the 

 shell strongly marked, agreeing w^ith that of ametra. Frontal organ with only a 

 small part of the stem projecting beyond the antenna. Terminal joint proximally much 



39* 



