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658 R. C. PUNNETT.is always complete after the first root. The ventral septum is a more conspicuous structurein this species than in most others of the genus. It is always found in the posterior partof the collar and may reach forwards over ^ of the collar length.Table 6.Pt.asymmetrica.No. of specimen(1)(2)(3)(4)(5)Proboscis ooelomVery smallas (1)Well markedbut smallas(l)Obliterated bymusclesCollar coelomMuch reducedAlmostobliteratedFairly spaciousVery smallWell markedVentral proboscis septumShort. Notnearly to tip ofstomochordNot to tip ofstomochordNot quite totip ofstomochordas (3)as(l)Dorso-ventral proboscis musclesAbsentas(l)as(l)as(l)as (1)Dorsal collar septumComplete after1st rootas(l)as (1)as(l)as(l)Ventral collar septumComplete inhind end ofcollaras (1)as(l)as(l)Complete inposterior ^ ofcollarRacemose organLarge butunlobulatedLarge andlobulatedas (1)Small andunlobulatedVery large andlobulatedDorsal proboscis muscle decussationWell marked.No ventral circularmusclesas(l)as(l)Not wellmarked. Noventral circularmusclesas(l)Dorsal roots*RRRRRrrRRRRRProboscis pores*LRLrIRIRIRNerve cordLength of post-branchial grooveLength of branchial regionLumen almostobliterated•23Lumen distinctin placesLumen distinctin places.Strong tendencyto obliteration•18as(l)•24as (1)Length of cornua x 100Length of collar24-520-947-340^52b-'Circumference of branchial oes.Circumference of ocsoph.oes.1-081-041-06Synapticula,Not more than 5The lumen of the collar cord is never continuous throughout. It may be present asa number of small cavities much broken up, or it may be practically absent, the cord shewing* See foot-note ou p. 64.5.