390 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.52. 



viz, one mesogastric, besides the one above mentioned, one urogas- 

 trio, two cardiac; the anterior of the gastric spines is the largest of 

 all. On the inner branchial region there is a short, nearly longitu- 

 dinal ridge, inclining a little inward anteriorly, and bearing a spine at 

 each end, the posterior spine the larger; on the right side there is a 

 small, low spine on the anterior slope of the posterior spine; this 

 accessory spine is wanting on the left side. A short but high, oblique 

 ridge runs to the postero-lateral margin, rises in a low spine ante- 

 riorly and terminates posteriorly in a strong spine which points back- 

 ward and outward, but is broken off at base. Short, low, obliquely 

 transverse ridges lead to two other lateral spines. All the lateral 

 marginal spines are broken off close to their origin. They appear to be 

 four in number, and with an hepatic and an outer orbital spine form 

 an almost semicircular row of six spines. The pterygostomian region 

 is produced well beyond the first of these spines and bears a spine 

 which is a little in advance of the angle of the orbit. 



Description of paratype. — Smaller than holotypo, with all spines 

 broken off, and with rostrum visible; this is small, triangular, surface 

 concave, with a deep, longitudinal furrow, tip rounded. 



Measurements. — Estimated width of carapace of holotype, at 

 widest part, in front of middle, 28 mm. Width of paratype at same 

 point, 18.6 mm.; approximate length of same, 20 mm.; width across 

 front and orbits, 8.6 mm. 



RelationsJiips. — This species resembles C. matutiforme Bell,* the 

 type-species of the genus, from the London Clay (Eocene) of the Isle 

 of Sheppey, England, in the presence of spines or tubercles on the 

 dorsal surface and spines on the margin. In pierrense the spines are 

 more numerous (6 marginal instead of 5), the front is simple instead 

 of bifid, and the pterygostomian region is much more prominent. 



As the specimens in hand show none of the appendages, I am unable 

 to improve upon the present grouping of tliis genus in the Matutinae. 

 The obliquely vertical surface in front of and below a line drawn 

 between the outer orbital spine and the pterygostomian or subhepatic 

 spine, is suggestive of the concave suborbital surface in many species 

 of Hepatus.- A prominent subhepatic spine exists often in the Oxy- 

 rhyncha, as in our common spider crabs, Lihinia.^ 



> Mono. Foss. Malac. Crast. Gr. Britain, pt. 1, 1857, p. 23, pi. 3, figs. 8-10. 

 2 Latreille, Hist. Nat. Crast., vol. 3, year 10 (1801-2), p. 22. 



8 See Proe. U. S. Nat. Mus., vol. 15, 1892, pi. 31, figs. 1, 2; the marginal spine behind the orbit is on 

 a much lower level than the succeeding spines. 



