BRYANT WAurvuu -•" 



MUSEUM OF ZOOLOGY 

 UNIVERSITY OF MICHIGAN 



NATURAL SCIENCES OF PHILADELPHIA. 217 



is, however, one Mexican species, one African, and one European. 

 H, arhustorum. The jaw of the last agrees with our species. 



The lingual membrane is long and narrow. Fig. 60 shows the 

 general arrangement of the teeth upon the lingual membrane. 

 The characters of the individual teeth are shown in mj plates. 

 I have selected H. Stearnsiana pi. XIII., fig. 3, to give an idea of 

 the teeth in successive transverse rows. Fig. a shows a group of 

 central and lateral teeth in two adjacent rows, b the transition 

 from laterals to marginals, c marginal teeth from near the outer 

 edge of the membrane. The central teeth have a base of attach- 

 ment much longer than wide, with incurved lower margin and 

 expanded lower lateral angles ; the upper margin broadly reflected ; 

 reflection short, stout, with subobsolete side cusps bearing no cut- 

 ting points, and a stout, long median cusp bearing a short, blunt 

 cutting point, which does not reach the lower margin of the base 

 of attachment ; the reflection with the median cusp is pear-shaped ; 

 in many species there is a duplicate line of reenforceraent parallel 

 to the upper margin of the base of attachment. The lateral teeth 

 are of similar type to the centrals, but are unsymmetrical by the 

 suppression of the inner, lower, lateral angle of the base of attach- 

 ment. The outer laterals have a side cusp and cutting point. 

 The transition from laterals to marginals is formed by the greater 

 proportional development of the cutting point, the lesser develop- 

 ment of the cusp ; the cutting point then becomes bifid, the re- 

 flection becomes more nearly the same size as the base of attach- 

 ment, and thus the true marginals are gradually reached. These 

 last are longer than wide, have a base of attachment smaller 

 than the reflection and cut away on its lower inner angle ; the 

 reflection is produced into one long, sharp, oblique, bifid cutting 

 point, the inner division the smaller, and one outer, much shorter, 

 sharp, rarely bifid cutting point. 



Most of the species examined agree in dentition with Stearnsi- 

 ana. Some have more blunt cutting points to their marginals, as 

 H. sequoicola (pi. XIY., fig. 5), but even on various parts of the same 

 membrane the marginals vary in this respect. In Kelletti, Stearn- 

 siana, tudiculata, arrosa, Traski, sequoicola, Ayresiana, redi7nita, 

 Nickliniana, ramentosa, exarata, I have failed to detect any side 

 cutting points to the central and inner lateral teeth. I found the 

 points, however, in H. ruficincla (pi. XIV., fig. 3). H. Town- 

 sendiana (pi. XVIII., fig. 8) has these cutting points and side 

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