KONGL. SV. VET. AKADEMIENS HANDLINGAR. r.AM) 34. \:<> 8. 69 



the lower end outwards, tho surface, which in the casl drawn is surrounded bj a mar- 

 ginal line, is directed sidewards againsf the broad latera] wings and i-- obscured b3 the 

 declivity formed by the groove. The same disposition of the maculse also occurs in Ptych. 

 glabrata. These two species consequently in this resped differ essentially From the other 

 four species which we have examined, hut there is for the resf no reason to make these 

 form different genera or subgenera. 



Pt. angustifrons Dalm. 



Pl. VI figs. 31— 3G. 



There are two varieties of hypostomas: onc broad fig. 32 and one more elongated 

 fig. 33. The maculse having a convex surface lie at the inferior end of the lateral grooves 

 prominent on a semicylindrical support, slightly inclining outwards. In the broad varietj 

 the}' are oblique (fig. 34) and in the elongated variety they are horizontal (fig. 35). In 

 a vertical section tig. 36 we have the same indications of a prismatic arrangement in the 

 macula? as in the Asaphi. The horizontal section does not represent so clear and dis- 

 tinct a reticulate structure as in the Asaphi, the prisms are much smaller. 



The cephalic eyes are composed of closely packed hexaedral prisms, the gradual 

 chauge from solid homogenous ones to those which are interiorly destroyed, only with 

 the exteriör form preserved is easily seen. The figure of a horizontal section (tig. 31) 

 gives a good idea of the peculiar destruction of the interiör of these prisms. In the 

 vertical section the prisms are not discernible. 



Pt. cincta Brögger? according to Friedr. Schmidt in Mus. Holm. 



Pl. VI figs. 37—39. 



The hypostoma which Brögger figures (II, pl. I fig. 2 a) as belonging to this species 

 is completely identical with that of Pt. angustifrons, while the specimens which Fr. Schmidt 

 has marked out as being the true Pt. cincta have a different hypostoma. The maculse 

 vary in the specimens, being in some placed horizontally or in a right angle to the 

 longitudinal axis of the hypostoma, in others, again, a little obliquely outwards. They 

 form prominent, free lying tubercles. It is from the superior face that the rudimentär v 

 lenses have left their traces, as seen in a longitudinal section (Hg. 39). It is consequently 

 this superior surface which is the macula proper. 



Pt. glabrata Ang. 



Pl. VI fig. 42. 



We have given a figure of tho elliptic acuminate macula 1 as seen on a cast of the 

 inside of a hypostoma, the same which is the original to fig. 14 in Br. II. 



K. Sv. Vet. Akad. IIhihH. Band 34 N:o 8. 9 



