60 PROCEEDINGS OP THE ACADEMY OF [1880. 



commonly two larger papillae before and a bare space behind them. 

 The gill (not retractile) consisting chiefly of several (usually 20-30) 

 tripinnate leaves, set in the form of a horseshoe. The head large, 

 veil-formed (semilunar), with produced and pointed side-parts, which 

 are adherent to the foot nearly to the point. The genital openings 

 not being a slit, but on a large tubercle. 



The cuticula of the oral aperture is thickened below, near the median 

 line, into a ledge ; and on the outside is a ring of hard papillae. 

 The buccal crop, connected through a petiolus with the foremost part 

 of the upper side of the bulbus pharyngeus, is drum-shaped ; on the in- 

 side clothed with a strong cuticula. The tongue has on the rhachis 

 short compressed lamellce, on each side of these is a very large up- 

 right plate with large compressed body and a hook which on the inside 

 is either plain or denticulated j at the outside of this plate is another, 

 compressed but much smaller and with a little rudimentary hook. The 

 salivary glands forming a short, coiled mass at each side of the root 

 of the oesophagus. The oesophagus without diverticle at its origin. 

 The spermatoduct (as in the Acanthodorides) very long ; the penis 

 short, its glans curved and clothed with a rather thick cuticula, but 

 otherwise not armed. The spermatocysta imbedded in the mucous 

 gland ; ^ the vagina short. 



About the biological relations of the animals belonging to this 

 group very little is hitherto known. Where the species occur, they 

 seem to be rather abundant in individuals (cf. about the Lam. 

 bilamellata, Collingwood, in Ann. Mag. Nat. Hist., 3 S. Ill, 1859, p. 

 463). The spawn of several species (L. bilamellata, L. diaphana, L. 

 inconspicua, L. aspera, L. depressa, L. pusilla) has been described 

 by Alder and Hancock, and that of a single species (Z. muricata) by 

 Sars, Meyer and Moebius, etc. The first stages of the development 

 of this last form have been followed by Sars ^ 



The group seems limited to the northern part of the Atlantic and 

 of the Pacific. To the same belong with certainty some properly ex- 

 amined species, and, besides, several others mentioned in the litera- 

 ture can, with more or less probability, be referred to it. 



' The spermatocysta has not been seen by Alder and Hancock. Cf. 1. c, 

 1852. PI. XIV, fig. 8 (p. 219). 



2 Archiv. fur Naturges, 1840 p. 210, Tab. 7. 



