PAUjSTA of the ST. JOHN GROUP. 41 



ObOLELLA (?) GEMMULA, u. sp. (PI. XII, figs. 8 a-c.) ' 



Ovate aci^miuate, sides somewhat straight in the posterior half, somewhat broadly 

 rouuded iu the anterior half of the shell. Test corueo-calcareous. 



Dorsal valve bluut, depressed at the umbo. Interior smooth except at the posterior 

 end, where, concealed in the bluut beak, is a short ridge, dividing the small scars of the 

 adductor muscles ; a small scar on each side of the valve close to the edge, and about one- 

 third from the beak marks the attachment of the adjustor muscle. Opposite this there 

 is a slight elevation or ridge on the median line of the valve. 



Ventral valve acuminate behind ; it has a small triangular area, with pedicel groove 

 and low beak. The interior of the valve has a ridge, most distinct iu the posterior third, 

 along the median line ; the part of the ridge appears double in some shells, but in others 

 only a single sharp ridge. On each side of this part of the ridge, but not extending its 

 full length, are the suboval scars of the adductor muscles. The central part of the shell 

 is occupied by a large bi-lobed sub-circular scar. The outer borders of these two scars or 

 depressions of the shell are defined by a sharp line, elevated in the middle of its length, 

 and there bent toward the centre of the shell. The margin of the valve appears flattened 

 and creuulated. 



Sculpture. — This consists of concentric ridges and lines, and of less conspicuous radi- 

 ating ridges. 



Size. — Length of ventral valve, 4J mm. ; width, 3|. The dorsal valve is one-half of 

 a millimetre shorter. 



Horizon and Localilij. — In a bed of fine grey shale iu the Dictyonema beds Div. 3 c at 

 Navy Island, St. John Harbour. 



Although in some respects resembling a Liugulella, there are in others such wide 

 differences iu this little shell that we have sought for relations to other genera, and 

 notably to Obolella. So far as cau be gathered from the descriptions of authors the .shell 

 substance in this genus is calcareous, though in regard to O. polita Mr. Hall speaks of 

 this as doubtful. In most of the species of this genus also the dorsal valve is shown 

 to possess an area at the hinge line. In this respect the new species differs, as the 

 area, if any exists, is very short. However, this does not appear to be of so much 

 moment as the best known species of Obolella had littoral habits, requiring a stronger 

 shell than would be needed for a species living iu deep, still water. A similar differ- 

 ence is observable between the species of Obolus described in this article and O. ApoUinis 

 of Russia. 



In the general form of the viisceral cavity, as well as in the details of its anatomy, 

 there are many points of resemblance to Obolella. The mesian ridge of the ventral valve 

 is one of these, extending as it does in its full strength somewhat beyond the bifid muscular 

 scars under the cardinal area ; and the incurved points of the bounding ridges of the vis- 

 ceral cavity is another. The peculiar depression along the posterior half of the median 

 ridge appears to correspond to the pit within the area of the ventral valve, seen in several 

 species of Obolella." A structure similar to this is seen in O. ambigua, and in O. politaihis 



' The lithographic plate is too coarse to show well the characters of these and the following species of 

 brachiopods. 



^ 0. gemma, 0. crasea and 0. chromatica. 



Sec. IV, 1891. 6. 



