[lambe] ON NEW SPECIES OF ASPIDERETES 15 



The peripheral edge is sharply rounded where free, becoming thinner 

 and more acute where it is scalloped ; at the bridges there is a decided 

 angulation. 



The shell is sculptured in a conspicuous manner by a combination 

 of nodes and ridges. In the longitudinal mid -line there is a ridge 

 along the length of the neural bones. In the more anterior neurals 

 this ridge may become double with minor oblique ridges and grooves 

 on each side. Slightly behind the centre of each of the four larger 

 costal scute areas there is a node, or swelling, from which radiate 

 well-marked ridges which tend to become nodular or elevated where 

 they terminate. Other minor swellings occur along the front peri- 

 pheral margin, and near the margin laterally and posteriorly. This 

 sculpture pattern is definite and gives an undulatory surface to the 

 carapace. 



The carapace is composed of the following bones: — in the mid-line, 

 the nuchal, a preneural, eight neurals, a suprapygal, and pygal; 

 on each side, eight costals; on the periphery, twelve marginals to each 

 side. The horny shields or scutes, as indicated by the grooves, or sulci, 

 were as follows: — in the central line, the nuchal scute and five verte- 

 brals; to each side, four large costal scutes with a small supernumerary 

 costal in front, and a small posterior one, making twelve costals in 

 all; eleven marginal scutes on each side, and between the larger 

 costals and the marginals three supramarginals of fair size. 



The nuchal bone is three times as broad as long, and is excavated 

 behind for the reception of the anterior edge of the preneural. This 

 latter is half as broad as the nuchal, and short from front to back. 

 The first neural is four sided and broadest in front. The second, 

 third, fourth and fifth neurals have six sides of which the two antero- 

 lateral ones are short; their greatest breadth is far forward at the 

 back termination of the short sides. The sixth neural is eight-sided 

 with four short sides of which two are antero-lateral and two postero- 

 lateral. The seventh neural is six-sided with two postero-lateral 

 short sides. The eighth neural is four-sided and broadest behind. 

 The suprapygal is lenticular in outline, of the same breadth as the 

 eighth neural, and three times as broad as long. The pygal is more 

 than three times as broad as long, and twice the breadth of the supra- 

 pygal which is received into an emargination of the front border of the 

 former bone. 



Of the eight costal bones the first is irregularly triangular, the 

 second, third, fourth, sixth and seventh increase in breadth (fore and 

 aft) distally, the fifth narrows to its distal end, and the eighth is of 

 irregular shape. 



The marginal bones are mostly subquadrangular in shape; 

 there is little difference in their length but they vary considerably 



