12 BULLETIN OF THE 



holes. The cups are often irregular and not very well developed, occurring in 

 several stages of growth. A complete cup is built up of a cruciform rod with 

 the curved arms united by a rim provided with several knobs. Sometimes 

 the cups almost form spheres. 



At the posterior end of the body, the skin is filled up with irregular large 

 plates, perforated with numerous holes ; these plates are partly simple, partly 

 composed of several superposed layers, so that each plate has the aspect of a 

 thick irregular network. The posterior end of the body also feels very rough 

 and hard to the touch. The anus is devoid of teeth. 



The pedicels have a small, more or less reduced terminal plate, but are 

 devoid of true supporting rods. The strong retractors are attached slightly in 

 front of the middle of the body. A single Polian vesicle and one madreporic 

 canal are present. Each genital bundle is very well developed, and consists of 

 numerous unbranched slender tubes. The calcareous ring is composed of ten 

 simple pieces, devoid of posterior prolongations. 



This species certainly bears a strong resemblance to Thyone (TJiyonidium ?) 

 lechleri, Lampert, but differs mainly in the shape of the deposits and the 

 calcareous ring. 



Habitat. Sandy Point, Strait of Magellan (Hassler Exp.); three specimens. 



Thyonidium moUe, Selenka. 



The tentacles vary greatly in number and size. The radial pieces of the 

 calcareous ring are slightly prolonged and bifurcate posteriorly. 

 Habitat. Payta, Peru (Hassler Exp.). Several specimens. 



Psolus operculatus, PouRXALfes. 



Figrure 4. 



In addition to the description of Pourtales, the following may be men- 

 tioned. As a rule the odd ambulacrum is naked, except at the anterior and 

 posterior extremities where a few pedicels are to be found ; but in two speci- 

 mens one or more pedicels are also placed at about the middle of that ambu- 

 lacrum. The sole is strengthened by numerous close-lying deposits of a more 

 or less marked symmetrical shape ; they consist of solid oval or roundish 

 slightly concave plates or cups, which usually are perforated with four holes, 

 and have the margin more or less deeply undulated from low outwardl}^ di- 

 rected knobs. In addition to the symmetrical cups, others are present more 

 or less developed and pierced with a varying number of holes. 



The largest complete specimen in the collection measures 37 mm. in length, 

 24 mm. in breadth, and about 11 mm. in height. The smallest has only a 

 length of 15 mm. In all the specimens I have seen, the mouth has five large 

 triangular scales, which, however, do not cover the opening completely, but 



