PSEUDOLIOCERAS. 81 



HlLDOOERATIOE. 1 



Genus — Pseudolioceras, 2 S. Buchman. 



{Type — Pseudolioceras compactile, Simpson sp.) 



Definition. — Discoidal, compressed, hollow- carinate ; whorls broad and sub- 

 convex, ornamented with subfalciform radii which approach the carina at an acute 

 angle. The ribs are distinct only on the outer area, not prominent, rather broad, 

 and rounded. The ventral area exhibits a very narrow space on each side of the 

 carina, which space is sometimes scarcely defined from the lateral area ; but when 

 the test is absent the ventral portion is an ill-defined, scarcely carinate, convex 

 area joining the two sides of the whorl. The carina is sharp, distinct, somewhat 

 prominent, and hollow. 3 When the test is absent, some slight indications of a 



1 Also substitute this word for Hildocera^'«« on p. 21, heading ; for reason see p. 125, et segr. 



2 \ptv8os, false. 



3 A " hollow-carina " is one which is partitioned off from the rest of the specimen by a spiral band 

 at its base. Such a carina was formed because the inner ventral portion of the animal in the last chamber 

 did not occupy the carina itself, but was attached to an extra internal partition which shut off the raised 

 carina. This partition-band was flat on its upper side and concave beneath. The two sides of the carina, 

 together with the partition-band, enclosed a subtriangular hollow space (now, of course, filled with 

 matrix or crystal), separated entirely from the air-chambers, and, for part of its length, from the animal. 

 The siphuncle does not lie within the carina of hollow-keeled Ammonites, but is situated beneath the 

 partition-band (Plate A, fig. 38). When the test is absent from hollow-keeled Ammonites, the core or cast 

 of the specimens is generally rounded on the ventral area, and gives no idea of the large carina which 

 the specimen would possess were the test uninjured (Plate A, fig. 38) ; but in some genera the ventral area 

 of the core shows a small indication of a carina (Plate A, fig. 47), which, however, bears no proportion 

 to the large carina actually possessed by the specimen. The ventral lobe, of course, embraces the 

 siphuncle, and is attached to the partition-band, but does not have any connection with the inner walls 

 of the carina. This carina, therefore, forms a separate hollow tube (the partition-band being the base), 

 which runs round the periphery of the Ammonite ; and the matrix in this hollow tube has sometimes 

 been mistaken for the siphuncle. (In some specimens the matrix with which this tube is now filled 

 contains a black substance.) 



In the solid-keeled Ammonites the structure of the carina is quite different. There is no trace of 

 a hollow tube, nor of a partition-band ; the ventral area of the core partakes of the shape of the test, 

 being carinated in proportion (Plate A, fig. 27) ; the siphuncle lies within the carina, and is embraced 

 by the ventral lobe, which is attached to the inner walls of the carina. 



It must, however, be particularly noticed that a part of the body-chamber of the hollow-keeled 

 Ammonites does not exhibit the hollow keel. The hollow tube is continued beyond the last air-chamber 

 for about one-fourth the length of the body-chamber. My specimens (species of various genera) seem 

 to show that at this point it ends suddenly, and they then become solid-keeled. Upon the body- 



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