NIAGAEA GROUP. 243 



and those laterally in contact dissimilar. The longitudinal groove is sinuated or lobed in the 

 same manner. A range of minute joints, or ossicula, partially fill this groove, diverging to the 

 bottom of each sinus or lobe, where the tentacula originate. These grooves from the four arras 

 do not meet at the apex of the body ; but the two from the anterior pair meet on the anterior 

 side of the summit, and those from the posterior pair meet on the posterior margin of the sum- 

 mit, and are thence connected together by a single straight groove in the direction of the back 

 and front of the body. When these grooves are occupied by the little ossicula, which do not 

 fill them entirely, they give a very beautiful appearance to the surface, diverging into the lobes 

 of the grooves and reaching the bases of the tentacula, of which a few of the lower joints still 

 remain, proving thcra to have been calcareous. 



I am unable to observe the reniform groove or pore on the right side near the apex, or any 

 orifice beyond the one noticed on the left side, except a minute elevation of a slightly darker 

 color just below that which I have termed the oral orifice. This point, much magnified, presents 

 scarcely a visible peculiarity ; but a farther enlargement shows it to be composed of minute 

 triangular plates, and that it is a miniature form of the ovarian orifice. In another specimen, 

 which is weathered, these minute plates are wanting ; and there is a small cavity visible, which 

 probably communicates with the interior : this therefore may be regarded as the anal orifice. 

 It will be seen from the arrangement of the arms, that the groove with ossicula communicating 

 between the pairs and across the apex, precludes the existence of a mouth in that position, 

 unless it be very minute ; and even then, there is no arrangement of parts to admit of its 

 existence. It should be noticed that the base of the tentaculum, in the angle at the divergence 

 of the arms of each pair, is larger than the others, and this may be of generic importance. 



The slight deviations in structure from the intercalation of a small plate between the first and 

 second series as shown in the diagram of structure, or the subdivision of one plate into three, 

 does not in any other respect affect the form or important characteristics of the animal, and can 

 not even be regarded as of specific importance. 



607. 1. APIOCYSTITES ELEGANS (n. sp.). 



PL. LI. Figs. 1 - 17. 



Cora^^Ye jipiocystites pentremitoides, Forbes, Mem. Geol. Survey of Great Britain, 1848, Vol. 

 ii, part ii, pag. 502, pi. xv. 



Body oblong oval, slightly compressed at the sides, composed of four series of plates, the 

 basal series consisting of four, the second five and the third six, while the fourth is not fully 

 ascertained ; arms four, consisting of an anterior and posterior pair, which are placed in shallow 

 grooves at the rounded angles, of the body, and rise above the plates on either side, extending 

 downward to the junction of the basal and second series of plates ; surface of the body and 

 plates of the arms ornamented by minute granules and larger tubercles, the latter often 

 coalescing and forming irregular ridges ; rows of granules often parallel to the margins of the 



