106 CARBONIFEROUS CEPHALOPODA OF IRELAND. 



me, making the margin subangular on one side.) The umbilical declivities being 

 rounded, there is no well-defined boundary between them and the sides into which 

 they merge. The whorls come into contact only upon the peripheral area, and 

 there is consequently no overlapping. 



The length of the body-chamber cannot be given with exactness, but it appears 

 to have occupied at least half a volution. The aperture has not been seen. The 

 last whorl detaches itself from the penultimate one in approaching the aperture. 



The septa, seen only on the sides of the shell (and there exposed by artificial 

 means), are 5 mm. apart where the diameter of the whorl is 11 mm. ; thus they 

 are, relatively to this, wide apart. The interior of the chambers is filled with 

 clear crystalline calcite, the deposit of which has nearly everywhere destroyed the 

 septa in the specimens before me. 



The siphuncle is considerably above the ceutre (PI. XXVI, fig. 3 c). 



The ornamentation consists of extremely fine longitudinal ridges, which, as in 

 other members of this genus, become obsolete upon the second volution. Cross- 

 ing the ridges is a series of equally fine transverse lines of growth, which at the 

 point of intersection of the two systems of lines form little nodes, which impart 

 a finely beaded appearance to the ornamentation viewed as a whole. The 

 ornamentation is so fine as to require magnifying to bring it out clearly. Beyond 

 its limits irregular lines of growth are developed, which in the adult shell are here 

 and there rather strongly' marked. Otherwise the shell may be regarded as quite 

 smooth except in the first whorl and part of the second. 



Dimensions. — Diameter of shell 90 mm. ; width of umbilicus 4" mm. ; height 

 of outer whorl 25 mm. (PI. XXVI, fig. o /*). 



A^nities. — From Discifoceras Lereilleauum, de Kon.,the present species is easily 

 distinguished by the absence of the numerous and regular transverse lines invariably 

 met with in the former, as well as by the much less prominent character of the 

 longitudinal ridges, which, as stated above, present the finely beaded appearance, 

 which is not the case in D. LereiUeanum, in which the longitudinal ornaments, as 

 far as they are developed, are much more conspicuous than the transverse ones. 

 D. ]\'ri(j}itii would, in fact, at first sight be taken for a perfectly smooth shell, 

 and it is not until the lens is brought into requisition that the fine ornaments of the 

 inner whorls are revealed. 



li'tmarks. — This species is quite common at Little Island, near Cork, but it is 

 rarely obtained undistorted, having generally an elliptical form with the peripheral 

 area pressed out of shape, making one side of the shell flatter than the other. An 

 uncompressed specimen is, however, shown in PI. XXVI, fig. 3 a. I have named 

 this species after my friend Mr. Joseph Wright, F.G.S., of Belfast. 



Localidis. — Little Island and ]Midleton, near Cork. 



