FROM THE INFERIOR OOLITE. 2C3 



Although the structure of the peristome in the Echinoconid^; led us to infer the 

 existence of jaws in the entire family, still we had only feeble traces of them in Ecldnoconus 

 albo-galerus, Klein, and Pygaster umbrella, Agass. Our discovery of these organs in 

 Holectypus depressus, Leske, is a fact new to science ; each jaw consists of two slender 

 branches united near the apex, and supports a long, slender, prismatic tooth (fig. \g). 



The anal opening is large and pyriform, with the apex directed towards the mouth ; 

 it occupies nearly all the space between the mouth and the border, and is therefore 

 situated entirely at the base of the shell (fig. 1 b) ; the direction of the apex of the vent 

 inwards, and its basal position, form important diagnostic characters, by which this 

 species is clearly distinguished from its congeners. The tubercles situated at the 

 base, are much larger and more fully developed than those on the upper surface (fig. 1/), 

 but instead of having a circle of granules around the areolas, they are separated laterally 

 from each other by sharp elevations of the test, the upper and under sides of the areolas 

 being bounded by crescents of granules (fig. If). 



Many spines are preserved in situ on the shell (fig. 1 g) ; they have a long, conical 

 head, with a prominent ring, and a slender, tapering stem, which is sculptured with 

 numerous longitudinal lines (fig. 1 h) ; the apex is blunted. Besides these primary spines, 

 which were articulated with the largest tubercles, I find the miliary granulation at 

 the base likewise possessed fine, hair-like spines, as they are observed in connection with 

 their granules among the larger spines at the under surface (fig. 1 g). 



Affinities and differences. — Holectypus depressus, Leske, may be regarded as the best 

 type of this genus. It is distinguished from H. hemisphaericus, Desor, by its more depressed 

 form, basal vent, and more acute marginal fold. The apex of the pyriform anal opening 

 is directed towards the mouth, whilst in H. hemisphdericus, it is just the reverse. 



It is distinguished from H. oblongus, Wright, by the form of the test, which is circular 

 or sub-pentagonal, whereas in that Coral Rag species it has an oblong shape ; the 

 tubercles on a portion of the inter-ambulacral plates form a single line of tubercles, 

 whilst in H. oblongus they are disposed in double lines on the same plate (fig. 3 d). 



Locality and Sir atigraphical position. — This urchin is found for the first time in the 

 Upper Ragstones of the Inferior Oolite, in the zone of Ammonites Parkinsoni, Sowerby. 

 I have collected it from the Trigonia Grit, wherever that bed is present, along the whole 

 range of the Cotteswold Hills, as at Dundry, Wotton-under-Edge, Stinchcombe, 

 Rodborough, Coopers, Birdlip, Shurdington, Leckhampton, and Sudeley Hills ; and at 

 Hampen, Naunton, and Stow-in-the-Wold, likewise in the Cornbrash near the Kemble 

 Tunnel, and in the neighbourhood of Cirencester, Gloucestershire. It is found rarely in the 

 Cornbrash near Chippenham, but abundantly in that formation near Trowbridge, Wilts, 

 whence I have a very fine series of large specimens in the finest preservation, collected 

 by Mr. Macniel. 



