CHO. — CRA.] 



BRACHIOPODA. 



687 



the internal cast. Type Chonetes fisclieri, 

 Norwood & Pratten. 



Ciionostrophia, Hall, 1892, Pal. N.Y., vol. 8, 

 p. 310. [Ety. rhonos, a cup ; strophe, 

 turning around.] Shell like a reversed 

 Chonetes, concavo-convex, the pedicel- 



,_■ valve being slightly convex about the 

 umbo, but becoming broadly concave 

 over the pallial region ; outline and 

 contour like Lepteena; valves ex- 

 tremely tenuous and compressed ; sur- 

 face covered with fine, alternating or 

 fasciculate striae. In the pedicel-valve 

 the upper margin of the cardinal area 

 bears a row of hollow spines of the 

 same structure and arrangement as in 

 Chonetes. The delthyrium is narrow, 

 and appears to be more or less com- 

 pletely closed. The teeth are quite 

 strong, and rest upon the bottom of the 

 valve; between them arises a low 

 median septum, extending one-third or 

 one half the length of the valve, divid- 

 ing a subcordate muscular area, the 

 outer margins of which are distinctly 

 elevated. In the brachial valve the 

 crural plates are united to form a 

 bilobed cardinal process. On the inner 

 surface it ends abruptly ; internal 

 pallial region finely papillose ; shell- 

 substance fibrous, punctate. Type Cho- 

 netes reversa, Whitfield- To the same 

 genus is referred Chonetes complanata, C. 

 dawsnni, and C. helderbrrgia, Hall, 1892, 

 Pal. N. Y., vol. 8, p. 353, Low. Held. 

 Gr. 



Christiana, Hall, 1892, Pal. N. Y., vol. 8, 

 p. 298. [Ety. proper name.] Shell re- 

 sembling Leptsena, usually longitudi- 

 nally elongated, sometimes semielliptical 

 in outline; normally concavo-convex; 

 surface smooth or covered with fine 

 radiating lines, crossed by stronger 

 concentric plications ; cardinal area of 

 the pedicel- valve high; delthyrium prob- 

 ably closed by a convex plate ; teeth 

 divergent, and from their bases extend 

 the elevated margins of two linguiform 

 muscular scars, traversing the shell al- 

 most the entire length ; these diductor 

 scars inclose two elongate adductors. 

 In the brachial valve the cardinal pro- 

 cess is bipartite, each of the lobes being 

 grooved behind; the crural plates are 

 long and divergent, terminating in 

 elevated extremities or crura. The 

 lower moiety of these plates is pro- 

 duced on each side of an elevated mus- 

 cular ridge, curving slightly inward on 

 the sides, then outward on approach- 

 ing the anterior margin of the valve, 

 each branch recurving and passing 

 backward, parallel to the median axis, 

 as far as the base of the cardinal pro- 

 cess. The interspaces are divided trans- 

 versely at about one-third their length 

 from the hinge-line, by a lower ridge. 

 The four areas thus inclosed represent 

 the posterior and anterior scars of the 



adductor muscles. Type Leptsena sub- 

 quadrata, Hall. 

 Clitambonites, Pander, 1830, Beitrage zur 

 Geognosie des russ. Reiches, p. 70. 

 [Ety. Mitos, a sloping place ; ambon, any 

 rising ; lithos, stone.] Shells with a sub- 

 semicircular marginal outline ; convex 

 or sub pyramidal ; hinge-line straight, 

 and forming the greatest diameter of 

 the shell ; pedicel-valve elevated ; cardi- 

 nal area high, vertical, or sometimes 

 incurved and crossed by a broad delthy- 

 rium, with a perforate deltidium ; dental 

 lamellae strongly developed, converging 

 and uniting in the median line ; median 

 septum about half the length of the 

 valve ; muscular impressions obscure ; 

 cardinal area developed in the brachial 

 valve, delthyrium filled with a callosity; 

 dental sockets large ; crural plates low ; 

 thickened transverse area in the um- 

 bonal region ; surface striate ; shell- 

 substance impunctate. Type Pronites 

 adscendens, Pander. It includes Orthis- 

 ina vernuili, Eichwald, and Hemipronites 

 americanus, Whitfield. 

 Conotreta, Walcott, 1890, Advance Sheets 

 Biological Soc. Washington. [Ety. 

 konos, cone ; treto*, perforated.] Struc- 

 ture calcareo corneous. Five narrow 

 ridges radiate from the apex toward 

 the front, on the internal side of the 

 dorsal or conical valve, the central one 

 of which joins the thickened apex, 

 • which is supposed to have been per- 

 forated by a siphonal tube. In Acro- 

 treta there is an elongated muscular scar 

 extending from each side of the si- 

 phonal tube obliquely forward. Type C 

 rusti, which is described at the same 

 place from the Trenton Gr. 

 Crania agaricina, C. pulchella, Hall, 1892, 

 Pal. N. Y., vol. 8, p. 180, Low. Held. Gr., 

 and C. granosa and C. favincola at same 

 place, Ham. Gr. 



blairi, S. A. Miller, 1892, Advance Sheets 

 18th Rep. Geo. Sur. Ind., p. 56, Chou- 

 teau limestone, and C. greenii from Up. 

 Held. Gr. 



columbiana, Walcott. 1888, Proc. U. S. Nat. 

 Mus. p. 441, Up. Taconic. Not defined 

 so as to be recognized. 



halli, Sardeson, 1892, Bull. Minn. Acad. 

 Nat. Sci., vol. 3, p. 328, Trenton Gr. 



radicans, see Strophaiosia radicans. 

 Craniella GShlert, 1888, Bull, de la Soc. 

 d'Etudes Scientif. d'Angers, p. 37. [Ety. 

 diminutive of Crania.] Shell somewhat 

 irregular; outline subcircular or sub- 

 quadrangular; ventral valve thin, ad- 

 hering by its entire surface ; dorsal 

 valve conoidal, more or less elevated ; 

 apex subcentral, posterior ; interior of 

 the dorsal valve without a well-defined 

 border ; impressions of the adductors 

 large, distinct, four in number, of which 

 the posterior two are quite distant, the 

 two subcentrals smaller, closely approxi- 

 mate or even confluent; from near each 



