396 E. W. MACBRIDE. 
the interruption of the somatic muscular system along the 
mid-dorsal and ventral lines and two dorso-lateral lines, the 
** submedian” lines in which the gonads open, and in three 
of the four genera also the gill-sacs; in Ptychodera, however, 
the outer gill-pores are situated dorsally to-this line. 
Both trunk and collar ceeloms are traversed by radiating mus- 
cular fibres, and in the trunk both dorsal and ventral mesen- 
teries persist, though in the collar they are partially absorbed. 
As has been mentioned above, a specialised dermis is absent, 
but there is a framework of connective-tissue cells ramifying 
amongst the proboscis muscles, and clothing the radiating 
muscles of the collar and trunk. 
CLASSIFICATION OF THE SPECIES. 
Pl. 30, figs. 2—7 are intended to give some idea of the range 
of variation in external form found in the species of Entero- 
pneusta. The main points to be noticed are the genital ridges 
of Ptychodera, small and inconspicuous in P. minuta, large 
and hiding the whole branchial region in P. erythrza, the 
liver saccules of Ptychodera and Schizocardium, the excessively 
short collar region of Glandiceps, and the immensely long 
proboscis of Balanoglossus Kowalevskii. 
Professor Spengel has described in all nineteen species, nine 
of which are new. As, however, eight of these are founded on 
the examination of single, more or less mutilated specimens, 
their specific value must remain for the present somewhat 
doubtful. The Enteropneusta have an almost cosmopolitan 
distribution. Specimens have been found in the Mediterra- 
nean, Atlantic shores of France, Channel Islands, Orkney 
Islands, White Sea, Japanese coast, eastern coast of United 
States, coast of Brazil, and coast of Peru. 
Spengel divides them into four genera, viz. Ptychodera, 
Schizocardium, Glandiceps, and Balanoglossus, all of which 
appear to me to be well founded. 
Ptychodera includes the oldest known Neapolitan species. 
