MELONECHINUS. 387 



This species was the first one described from Great Britain, and, differs from other Euro- 

 pean species in its robust size and number of interambulacral columns; and it differs from all 

 American species in which the exterior of the test is known by the absence of the melon-like 

 ribs. 



Lower Carboniferous Limestone, Clitheroe, Lancashire, Museum of Practical Geology 

 Collection, holotype 6,577; paratype 6,578. Keeping (1876, p. 399) says that these specimens 

 are from the Carboniferous Limestone of Derbyshire, but this is probably a mistake, as the 

 locality given is taken from the original label, and other specimens lithologically identical are 

 known from the Clitheroe locality. Clitheroe, Lancashire, Sedgwick Museum, Cambridge, 

 England, Collection 18, 19, 20; Coplaw, Clitheroe, Lancashire, Museum of Practical Geology, 

 16,303; between Clitheroe and Chatburn, Lancashire, H. L. Hawkins Collection; Vallis, near 

 Frome, Somerset, British Museum Collection (two specimens) E 1,400; Thornton-in-Craven, 

 Yorkshire, British Museum Collection E 9,540. 



The holotype, which is the original of Keeping's figures, is in the Museum of Practical 

 Geology Collection 6,577. A photograph of this specimen taken for me through the kindness 

 of Dr. Kitchin is in part reproduced as Plate 58, fig. 4. It is a large slab covered with numerous 

 dissociated interambulacral plates and twelve more or less complete fragments of ambulacral 

 areas, part of which are turned over so that they are viewed from within. The hexagonal 

 interambulacral plates measure about 8 mni. in width by 6 mm. in height and 4 mm. in thick- 

 ness. The external views of the ambulacra show no indication of a melon-like ridge. Several 

 of the fragments have six columns of plates, indicating a complete section of a half-area; pore- 

 pairs are in peripodia in the outer portion of each plate, and some of the plates have tubercles 

 and spines in place. In the ambulacra as seen from the interior the plates are more angular, 

 being nearly or quite hexagonal in this view, and the pore-pairs are near the middle of each 

 isolated plate, which is gently curved toward the interior of the test, as shown in Plate 59, 

 fig. 8, which was, however, drawn from another specimen. 



The second specimen in the Museum of Practical Geology Collection 6,678, is labeled as 

 Keeping's second type. It is evidently the specimen he referred to (1876, p. 398), although he 

 states that it is in the British Museum. Dr. Bather, after careful search, found no such speci- 

 men in the British Museum, and evidently the statement was a mistake or the specimen has 

 since been transferred to the Museum of Practical Geology. It measures 100 mm. in height 

 and 75 to 100 mm. in width, corresponding with Keeping's description. Structurally, it is the 

 most nearly complete specimen known. A photographic figure, which I owe to the kindness 

 of Dr. Kitchin, is given in Plate 58, fig. 3, and a drawing in Plate 59, fig. 5. The ambulacrum 

 shows six columns of the left half-area and some occluded and isolated plates of the right half- 

 area. The interambulacrum has a right adambulacral column and five columns of hexagonal 

 plates. In the figure I have added a left adradial coUunn, but there mav have been more 



